HAWASSI-AB MODELLING AND SIMULATION OF FULLY DISPERSIVE NONLINEAR WAVES ABOVE BATHYMETRY

Ruddy Kurnia

Samenstelling promotiecommissie: Voorzitter en secretaris: prof. dr. P. M. G. Apers

University of Twente

Promotor prof. dr. ir. E. W. C. van Groesen

University of Twente

Leden prof. dr. S. A. van Gils prof. dr. A. E. P. Veldman prof. dr. ir. R. H. M. Huijsmans prof. dr. F. Dias prof. dr. B. Jayawardhana dr. ir. T. Bunnik

University of Twente University of Twente Delft University of Technology University College Dublin, Ireland University of Groningen MARIN

The research presented in this dissertation was carried out at the Applied Analysis group, Departement of Applied Mathematics, Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) of the University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research (NWO) and partly funded by the Ministry of Economic Affairs (project number 11642).

c 2016, Ruddy Kurnia, Enschede, The Netherlands Copyright Cover: Erika Tivarini, www.erikativarini.carbonmade.com Printed by Gildeprint, Enschede isbn 978-90-365-4039-1 doi 10.3990/1.9789036540391 http://dx.doi.org/10.3990/1.9789036540391

HAWASSI-AB MODELLING AND SIMULATION OF FULLY DISPERSIVE NONLINEAR WAVES ABOVE BATHYMETRY

DISSERTATION

to obtain the degree of doctor at the University of Twente, on the authority of the rector magnificus, prof. dr. H. Brinksma, on account of the decision of the graduation committee, to be publicly defended on Friday 19 February 2016 at 16:45

by

Ruddy Kurnia born on the 1th of May 1987 in Bandung, Indonesia

Dit proefschrift is goedgekeurd door de promotor prof. dr. ir. E. W. C. van Groesen

To my parents

Summary

Water waves propagating from the deep ocean to the coast show large changes in the profile, wave speed, wave length, wave height and direction. The fascinating processes of the physical wave phenomena give challenges in the study of water waves. The motion can exhibit qualitative differences at different scales such as deep water versus shallow water, long waves versus short waves. Therefore, the existing mathematical models are restricted to the limiting cases. This dissertation concerns the development of an accurate and efficient model that can simulate wave propagation in any range of wave lengths, in any water depth and moreover can deal with various inhomogeneous problems such as bathymetry and walls, leading to wave structure interactions. The derivation of the model is based on a variational principle of water waves. The resulting dynamic equations are of Hamiltonian form for wave elevation and surface potential with non-local operators applied to the canonical surface variables. The Hamiltonian is the total energy, i.e the sum of kinetic energy and potential energy. Since the kinetic energy cannot be expressed explicitly in the basic variables an approximation is required. The corresponding approximated Hamiltonian leads to approximated Hamilton equations. The approximate Hamilton equations are expressed in pseudo-differential operators applied to the surface variables. The pseudo-differential operator has a physical interpretation related to the phase velocity. The phase velocity as function of wave length is specified by a dispersion relation. Dispersion is one of the most important physical properties in the description of water waves. Accurate modelling of dispersion is essential to obtain high-quality wave propagation results. Using spatial-spectral methods and a straightforward numerical implementation, accurate and fast performance of the model can be obtained. Moreover, the spatialspectral implementation with the global pseudo-differential operators or a generalization with global Fourier integral operators (FIO) can retain the exact dispersion property of the model. Other numerical implementations with local differential operators such as finite difference or finite element methods require that the dispersion is approximated by an algebraic function. Such an approximation leads to restrictions on the range of wave lengths that are modelled correctly. To deal with practical applications, several extensions of the model are imple-

viii mented. The model with localization methods in the global FIO can deal with localized effects such as breaking waves, partially or fully reflective walls, submerged bars, run-up on shores, etc. The inclusion of a fixed-structure in the spatial-spectral setting is a challenging task. The method as presented here perhaps serves as a first contribution in this topic. An extended eddy viscosity breaking model and a breaking kinematic criterion are used for the wave breaking mechanism. The extended eddy viscosity breaking model can deal with fully dispersive waves. The kinematic breaking criterion prescribes that a wave will break when the horizontal particle speed exceeds (a fraction of) the crest speed. A universal or deterministic value of this parameter is not known yet. In many applications, such as the calculation of wave forces on structures, requires information of interior flow properties. A method to calculate the interior flows in a post-processing step of the Boussinesq model is described. Performance of the model is shown by comparing the simulation result with measurement data of various long crested cases of breaking and non-breaking waves. The model has been extensively tested against at least 50 measurement data. Moreover, 30 measurement data of wave breaking experiments were designed by the accurate wave model. It will be shown that an efficient and accurate code can optimize the experiments. The models and methods presented in this dissertation have been packaged as software under the name HAWASSI-AB; here HAWASSI stands for Hamiltonian Wave-Ship-Structure Interaction, while AB stands for Analytic Boussinesq. More information of the software can be found on http://hawassi.labmath-indonesia.org.

Samenvatting

Watergolven vertonen gedurende hun reis van de diepe oceaan naar de ondiepe kust grote veranderingen in vorm, snelheid, golflengte en richting. De fascinerende processen van deze fysische golfverschijnselen leiden tot uitdagend onderzoek. De beweging kan leiden tot kwalitatieve verschillen op verschillende schalen van waterdiepte en golflengte. Daarom zijn veel wiskundige modellen beperkt tot limiet gevallen. Dit proefschrift behandelt het ontwikkelen van een nauwkeurig en efficint model dat de voortplanting kan beschrijven en berekenen van golven met willekeurige golflengte boven willekeurige waterdiepte, zelfs in interactie met inhomogeniteiten zoals veranderende bodemdiepte of de aanwezigheid van wanden. De afleiding van het model is gebaseerd op een variatieprincipe voor watergolven. De resulterende dynamische vergelijkingen zijn een Hamiltons systeem voor de golfhoogte en de oppervlakte potentiaal met niet-lokale operatoren die werken op deze canonieke oppervlakte variabelen. De Hamiltoniaan is de totale energie, de som van kinetische en potentiele energie. Omdat de kinetische energie niet expliciet uitgedrukt kan worden in de basisgrootheden is een benadering vereist. De daarmee corresponderende Hamiltoniaan leidt tot de benaderde Hamilton vergelijkingen. Deze vergelijkingen zijn uitdrukkingen met pseudo-differentiaal operatoren toegepast op de oppervlakte variabelen. Deze operator is fysisch gerelateerd aan de fase-snelheid. Deze snelheid wordt bepaald door de golflengte via de zogenaamde dispersie-relatie. Dispersie is een van de meest belangrijke eigenschappen in de beschrijving van watergolven, en een goede benadering is essentieel om goede resultaten te verkrijgen voor golfvoortplanting. Ruimtelijk-spectrale methoden en een directe numerieke implementatie leiden tot nauwkeurige en snelle resultaten. Bovendien kan door de ruimtelijk-spectrale implementatie van de globale pseudo-differentiaal operatoren, of de generalisatie naar Fourier integraal operatoren (FIO), de exacte dispersie-eigenschappen van het model bewaard worden. Overige numerieke implementaties met lokale differentiaal operatoren, zoals eindige-differentie of eindige-element methoden, vereisen een benadering van de dispersie met een algebrasche functie, hetgeen tot beperkingen leidt van de golflengten die nauwkeurig voortgeplant worden. Om praktische problemen aan te kunnen pakken zijn meerdere uitbreidingen geimplementeerd. Localisatie-methoden voor de globale FIOs maken het mogelijk

x gelocaliseerde effecten te simuleren, zoals brekende golven, gedeeltelijk of volledig reflecterende wanden, onderwaterdrempel, oploop op de kust, etc. Dit toevoegen van vaste structuren in ruimtelijk-spectrale modellen is een uitdagende taak; de bijdragen daaraan die hier worden gepresenteerd zijn misschien de eersten van dit soort. Een eddy-viscositeits breking model met een kinematisch breking criterium worden gebruikt voor golfbreking; het brekingmodel is uitgebreid zodat het bruikbaar is voor volledig dispersieve golven. Het kinematisch criterium zorgt ervoor dat een golf breekt als de horizontale deeltjessnelheid groter is dan een fractie van de snelheid van de golftop. Een universele of deterministische waarde voor die fractie is nog niet bekend. In veel toepassingen zijn de interne stromingssnelheden van belang, bijvoorbeeld voor de berekening van krachten op structuren. Er wordt een methode gepresenteerd om de interne stroming te berekenen nadat de oppervlaktegrootheden van het Boussinesq model zijn berekend. De prestaties van het model zijn aangetoond voor meer dan 50 gevallen door berekende resultaten te vergelijken met meetdata van experimenten van langkammige golven met of zonder breking. Bovendien zijn met de software 30 experimenten van golfbreking ontworpen, waarmee aangetoond wordt dat daarmee het experimenteren geoptimaliseerd kan worden. Het model inclusief alle nieuwe methoden is als software beschikbaar onder de naam HAWASSI-AB. De afkorting HAWASSI staat voor Hamiltonian Wave-ShipStructure Interaction, en AB voor Analytic Boussinesq; meer informatie is te verkrijgen op http://hawassi.labmath-indonesia.org.

Contents

Summary

vii

Samenvatting 1 Introduction 1.1 A historical note on the study of water 1.2 Variational water wave modelling . . . 1.3 Contributions in this dissertation . . . 1.4 Outline of the dissertation . . . . . . .

ix

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1 3 6 9 11

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13 14 15 16 17 20 21 21 23 25 26 27 27 28 28 36 41

3 Localization for spatial-spectral implementations 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Spatial-spectral modelling within the Hamiltonian structure . . . . .

43 44 45

waves . . . . . . . . . . . .

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2 High order Hamiltonian water wave models 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 2.2 Variational wave description . . . . . . . . . . . . . 2.2.1 Hamiltonian formulation . . . . . . . . . . . 2.2.2 Consistent approximations . . . . . . . . . . 2.2.3 Hybrid Spatial Spectral implementation . . 2.3 Wave-breaking model . . . . . . . . . . . . . . . . . 2.3.1 Eddy-viscosity model . . . . . . . . . . . . . 2.3.2 Kinematic breaking criterion . . . . . . . . 2.3.3 Alternative viscosity model . . . . . . . . . 2.4 Numerical implementation . . . . . . . . . . . . . . 2.4.1 Damping zones . . . . . . . . . . . . . . . . 2.4.2 Nonlinear wave generation . . . . . . . . . . 2.5 Simulation results . . . . . . . . . . . . . . . . . . 2.5.1 Irregular wave breaking over a flat bottom . 2.5.2 Wave breaking over a bar . . . . . . . . . . 2.6 Conclusion and remarks . . . . . . . . . . . . . . .

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xii

CONTENTS

3.3

3.4

3.5

3.2.1 Hamiltonian structure . . . . . . . . . . . . . . . . . . . 3.2.2 Limiting cases . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Second order accurate approximation above bathymetry 3.2.4 Wave breaking and bottom friction . . . . . . . . . . . . 3.2.5 Internal flow and pressure . . . . . . . . . . . . . . . . . Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Partially reflecting wall . . . . . . . . . . . . . . . . . . 3.3.2 Frequency dependent reflecting wall . . . . . . . . . . . 3.3.3 Run-up on coast . . . . . . . . . . . . . . . . . . . . . . Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Irregular waves running up a slope . . . . . . . . . . . . 3.4.2 Irregular wave breaking over a bar . . . . . . . . . . . . 3.4.3 Harmonic breaking wave running up a coast . . . . . . . 3.4.4 Wave-wall interactions . . . . . . . . . . . . . . . . . . . 3.4.5 Dam-break problem . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Design of wave breaking experiments and 4.1 Introduction . . . . . . . . . . . . . . . . . 4.2 Experimental set up . . . . . . . . . . . . 4.3 Simulation model . . . . . . . . . . . . . . 4.4 Design and reconstruction . . . . . . . . . 4.4.1 Design cases . . . . . . . . . . . . 4.4.2 Reconstruction cases . . . . . . . . 4.5 Conclusions . . . . . . . . . . . . . . . . .

a-posteriori . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46 47 48 49 50 51 51 52 52 53 53 55 57 59 63 64 65 65 66 67 68 68 70 71

5 Conclusions and recommendations 5.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . .

75 75 76

Appendix A Supplementary files of the experiments A.1 The characteristic quantities of the designed waves . . . . . . . . . . A.2 Comparison of experiments and a-priori simulations . . . . . . . . . A.3 Comparison of experiments and a-posteriori simulations . . . . . . .

77 77 79 82

Bibliography

113

Acknowledgments

119

About the author

121

Chapter

1

Introduction

Figure 1.1: The Great Wave off Kanagawa, by Katushika Hokusai (18th century) (source: www.wikipedia.org)

Ocean waves are fascinating. The wind blowing over the sea surface generates wind waves. During storms, waves can become very high and develop foamy crests with very complex patterns. Waves approaching the shore get higher and steeper and may break to form waves that are spectacularly used by surfers. The breaking of large oceanic waves has drawn the most attention of human beings to observe this magnificent phenomenon. These natural processes have repeatedly been the themes in paintings. The Great Wave off Kanagawa (Fig. 1.1) is a well-known paintings, published in 18th century by Katsushika Hokusai. The wave has been discussed in scientific notes of [Cartwright and Nakamura, 2009, Dudley et al., 2013]. It is stated that the location of the wave is estimated to be 3 km offshore Tokyo Bay. The estimated wave height of around 10 m leads to the conclusion that this would be a wave of exceptionally large amplitude for this area and would likely be a rogue

2

Introduction

or freak wave. No less important are the scientific studies or concept of the wave phenomena and the ocean as well. For thousands of years, people have been depending on the ocean as a source of food and mineral, and as relatively easy medium for transport of people and goods. Nowadays, with developing of knowledge and technology, the ocean gives even more benefits. Resources of renewable energy such as wind farms, tidal and wave energy are mainly located in coastal areas. Moreover, coastal areas are centres of industrial activities, products and therefore money flows into countries through ports. This leads to the fact that half of the world population lives less than 150 km from the coast.

Figure 1.2: At the left: a photo taken on January 5, 2005 of the devastated district of Banda Aceh, Indonesia in the aftermath of the December 26, 2004 tsunami. Credit: Choo Youn-Kong/AFP/Getty Images. Source: theatlantic.com. At the right: Tsunami wave approaches Miyako city in Japan on 11 March 2011. Credit: Mainichi Shimbun /Reuters. Source: reuters.com.

Figure 1.3: At the left: A rogue wave reaching a height of 18 m hit a tanker headed south from Valdez, Alaska in February 1993. Credit: Captain Roger Wilson, NOAA National Weather Service Collection. At the right: The surface elevation time history recorded at the Draupner platform, which includes the New Year Wave. Source: [Adcock et al., 2011].

Apart from the profits, waves can also give problems. High waves during storms or caused by bathymetry or by collision against constructions or by undersea earthquakes can do great harm to ships, constructions and to people living near the coast.

1.1 A historical note on the study of water waves

3

On 26 December 2004, a Mw 9.1 undersea megathrust earthquake at the west coast of northern Sumatra, Indonesia generated a series of devastating tsunamis along the coasts of the Indian ocean. The series of waves reached the coasts of Banda Aceh (northwest corner of Sumatra) within 15 min after the earthquake, thus inundating 100 km2 of land. The waves were 5-30 m high at the coast and runup to 51 m and 6 km inland [Paris et al., 2007]. The reported number of casualties were approximately 230.000 killed in Indonesia, at least 29,000 killed in Sri Lanka, more than 10,000 in India, more than 5,000 in Thailand, and 82 killed in Maldives, and more than 22,000 are still missing [Kawata et al., 2005]. On 11 March 2011, a Mw 9.0 earthquake in the Pacific ocean close to Tohoku generated tsunami waves. The waves inundated the area with wave heights up to 15 m, runup height reached over 39 m and 6 km inland. Over 14.000 people were reported as dead and over 11.000 were missing [Mimura et al., 2011]. Furthermore, extreme waves, also known as rogue waves or freak waves, have been major causes of numerous accidents of oil-platforms and ships. Practically, a rogue wave is expected to be at least twice larger than the significant wave height. In February 1993, a rogue wave in the Gulf of Alaska was photographed by Captain Roger Wilson [Wilson, 1993]. The wave was reaching a height of 18 m above 7.6 m water depth. The rogue wave hit a tank ship on the starboard side when the ship was heading to south from Valdez, Alaska. On 1 January 1995, the ”New Year wave” was recorded in the North Sea at the Statoil-operated ”Draupner” platform [Adcock et al., 2011]. The Draupner wave was the first rogue wave to be detected by a measuring instrument. It was recorded that the crest height was 18.6 m, wave height 25.6 m above 70 m water depth. Fortunately this wave did not cause substantial damage, but attracted attention of the scientists to this problem. Since then, numerous accidents of oil-platforms and ships have been linked to the rogue wave occurrence. Nikolkina and Didenkulova [2011] collected evidence of rogue wave existence during the 5 year period, 2006-2010. From the total of 131 reported events, 78 were identified as evidence of rogue waves. Only events associated with damage and human loss were included. It is also stated that the extreme waves cause more damage in shallow waters and at the coast than in the deep sea. Therefore, a sustainable and safe development of the oceanic and coastal areas is of paramount importance. The fascination and the practical relevance have been motivating extensive study of water waves, probably as long as people live on earth but certainly in the past centuries. The past and recent studies of water waves are summarized in the following sections. Section 1.1 summarizes the extensive study in the past centuries, and Section 1.2 gives a description of variational water wave modelling. Highlights of the contributions of this dissertation are presented in Section 1.3. The outline of the dissertation will finish this chapter.

1.1

A historical note on the study of water waves

The water wave problem in fluid mechanics has been known since more than three hundreds years [Craik, 2004]. In 1687, Isaac Newton attempted a theory of water

4

Introduction

waves with an analogy of a fluid oscillations in a U-shaped tube. He correctly deduced that the frequency of deep-water waves must be proportional to the inverse of the square root of the breadth of the wave. In 1757, Leonhard Euler published a physically and mathematically successful description of the behaviour of an idealized fluid (inviscid flow). These Euler equations represent conservation of mass (continuity) and momentum. The Euler equations became the foundation of a realistic description of water which was derived 65 years later by Claude Navier. That is now known as the Navier-Stokes equations. Pierre-Simon Laplace (1776) derived a fundamental equation of tidal motion. He focused on free surface propagation, which only occurs if the cause of the wave is localized in space and time. This leads to the general initial value problem: Given any localized initial disturbance of the liquid surface, what is the subsequent motion? Cauchy and Poisson later addressed this problem. Later, Joseph Louis Lagrange (1781) also worked on the governing equation of linear water waves and obtained the solution in the limiting case of shallow water. He found that the speed of propagation of waves will be independent of wavelength and proportional to the square root of water depth; that is (gh)1/2 where g is the gravitational acceleration and h the water depth. In December 1813, the French Acad´emie des Sciences announced a mathematical prize competition on wave propagation on infinite depth. In 1816 Cauchy won the prize and his work was published in 1827. Independently, Poisson, who was one of the judges, deposited a memoir of his own work that was published in 1818. The Cauchy-Poisson analysis is now acknowledged as an important milestone in the mathematical theory of initial-value problem. Cauchy employed Fourier transform in analysing the Laplace equation for the velocity potential Φ(x, y, z) with x, y the horizontal coordinates and z the vertical coordinate ∂2Φ ∂2Φ ∂2Φ + + =0 ∂x2 ∂y 2 ∂z 2

(1.1)

incorporating the linearized free surface condition, with g the acceleration of gravity, ∂2Φ ∂Φ +g = 0. 2 ∂t ∂z

(1.2)

Cauchy then takes the second time-derivative of Eq. 1.2 as 2 ∂3Φ ∂3Φ ∂4Φ 2∂ Φ = −g = g . = −g ∂t4 ∂t2 ∂z ∂z∂t2 ∂z 2

Using Eq. 1.1 Cauchy’s equation is given by 2 ∂4Φ ∂ Φ ∂2Φ = 0. + g + ∂t4 ∂x2 ∂y 2

(1.3)

(1.4)

For a periodic wave of form exp[i(kx x + ky y − ωt)], the correct dispersion relation of deep-water waves can be obtained as ω 2 = g(kx2 + ky2 )1/2 .

1.1 A historical note on the study of water waves

5

However, Cauchy’s equation is only valid in the case of infinite depth since the bottom condition is neglected. In 1834, solitons, waves that propagate with constant speed and constant shape, were observed for the first time by the British scientist John Scott Russell. He was watching a barge being towed along a canal between Glasgow and Edinburg. On its sudden stop, a wave was observed, that propagated for nearly a mile with only little change of form. This phenomenon inspired him to perform experiments. Substantial reports by Russell and Robinson were published in 1837 and 1840. Russell wrote a brief supplementary report (1842) and then his major ”Report on Waves” (1844). Later, Boussinesq in 1872, and Korteweg and de Vries in 1895 produced theoretical results of the soliton wave. In 1841, George Biddel Airy published an influential article ’Tides and Waves’. His work became a major contribution of water wave theory. He gave a complete formulation of linear propagation of gravity waves. In his formulation, an impermeable boundary-condition was taken into account. The formulation is given as follows ∂2Φ ∂2Φ ∂2Φ + + = 0 for − h ≤ z ≤ 0 (1.5) ∂x2 ∂y 2 ∂z 2 ∂Φ + gη = 0 for z = 0 (1.6) ∂t ∂Φ ∂η = for z = 0 (1.7) ∂t ∂z ∂Φ = 0 for z = −h (1.8) ∂z in which Φ is the fluid potential, η the surface elevation, h the water depth and g the gravity acceleration. Airy’s equations represent incompressible and irrotational flow in the interior (Eq. 1.5), a dynamic free surface condition (Eq. 1.6), a kinematic free surface condition (Eq. 1.7) and an impermeable bottom condition (Eq. 1.8). Observe that the free surface conditions are actually the Cauchy condition (Eq. 1.2). Airy’s linear theory produces a correct dispersion relation for a propagating q monochromatic wave, η(x, y, t) = a cos(kx x+ky y −ωt) with a the amplitude, k = kx2 + ky2 the wave number and ω the angular frequency. The dispersion relation of wave propagation above a depth h is given by ω 2 = gk tanh(kh).

(1.9)

The dispersion relation also tells that the wave speed (which is the quotient of ω and k) depends on wavelength. As a consequence, the shorter waves travels slower. The work of Airy on the linear wave theory and the remarkable experiments of Russel motivated Stokes to investigate the water wave problem. In 1847, Stokes published his work on nonlinear wave theory that is accurate up to third order in wave steepness (k.a). He showed surface elevation η in a plane wavetrain on deep water could be expanded in powers of the amplitude a as 3 1 η(x, t) = a cos(kx − ωt) + ka cos 2(kx − ωt) + (ka)2 cos 3(kx − ωt) + · · · 2 8

6

Introduction

where ω 2 = gk 1 + (ka)2 + · · · the nonlinear dispersion. As a consequence of the nonlinear dispersion, the steeper the wave the faster it travels. He also showed that a wave with maximum height has a crest angle of 120◦ . The nonlinear effect influences the wave shape with sharp and higher crest and flatter at the trough. As a response to the observation and the experiment of soliton wave by John Scott Russel, Boussinesq [1872] derived equations that are now known as the Boussinesq equations. Boussinesq simplified the Euler equations for irrotational, incompressible fluid. He approximated the depth dependence of the Laplace equation in the interior fluid potential. In the approximation, a Taylor expansion up to a certain order around still water level is applied at the velocity potential function with incorporating the frequency dispersion. That leads to bi-directional and dispersive dynamic equation for the surface elevation and the velocity. These ’classical’ Boussinesq equations are valid for weakly nonlinear and fairly long waves. Of major importance is the fact that the whole dynamics is expressed solely by quantities at the surface, without any explicit equations for the interior flows. Nowadays, therefore, such models are more generally called Boussinesq (type of) equations. Korteweg and de Vries [1895] derived a simplified Boussinesq equation. The simplification was obtained in such a way that the bi-directional dynamic equations lead to one unidirectional dynamic equation. The KdV equation is valid for weakly nonlinear and weakly dispersive long waves and can be expressed as ηt + (c0 + c1 η)ηx + νηxxx = 0,

(1.10)

where c0 , c1 and ν are constants. The KdV equation has the same properties as the Boussinesq equation that both have (periodic) cnoidal and soliton profiles as solution. These theoretical results answered the observation and the experimental result of solitons by Scott Russel.

1.2

Variational water wave modelling

Many mathematical models of surface gravity wave have been developed recently. Most of the effort is to improve the accuracy of the model in terms of dispersion and nonlinear properties. A fascinating feature of the study of water waves is that the motion can exhibit qualitative differences at different scales such as deep water versus shallow water, long wavelength versus short wavelength. Therefore the existing wave models were constructed by various approximations to the limiting cases. In shallow water, there are equations of Boussinesq [1872], Korteweg and de Vries [1895], Benjamin et al. [1972], Serre [1953], Green and Naghdi [1976], Camassa and Holm [1993], and others. On finite depth and deep water, there are equations of [Stokes, 1847], nonlinear Schr¨odinger type of Dysthe [1979], Peregrine [1983] and others. Generally, these equations are valid for a limited range of the the relative water depth (kh, in which k the wave number, h the water depth). Most of the models were derived using some perturbation techniques that are valid for relatively small amplitude. However, in many applications it is desired to use a wave model that is uniformly valid for all depths and also accurate for large amplitudes. To that end, a different

1.2 Variational water wave modelling

7

approach of modelling, the so-called variational formulation is used in this work. In this section, the development of the variational formulation of water waves is summarized. Luke [1967] formulated a Lagrangian variational description of the motion of surface gravity waves on an incompressible and irrotational fluid with a free surface as Z Z Z η 1 2 ∂t Φ + |∇3 Φ| + gz dz dx. CritΦ,η P(Φ, η) dt where P(Φ, η) = 2 −h (1.11) The variables in this variational principles are the surface elevation η (depending on the two horizontal dimensions x and y) and the fluid potential Φ inside the fluid, so depending on horizontal and vertical dimensions. Note that this is a ’pressure principle’ since the integrand P denotes the pressure in the fluid, according to Bernoulli’s formulation of the Euler equation for irrotational fluid. The pressure principle has been remarked before by Bateman [1929] but without considering variations of the free surface η. The following is a derivation of the water wave problem from the Luke’s Lagrangian functional. The vanishing of the first variation of the functional with respect to variation δΦ in Φ leads to Z η Z Z dt dx ∂t (δΦ) + ∇3 Φ · ∇3 (δΦ) dz = 0. −h

It can be rewritten by applying Leibniz’s integral rule for the first term Z η Z η ∂t (δΦ) = ∂t (δΦ) dz − (δΦ)z=η ∂t η − (δΦ)z=−h ∂t h −h

−h

and the use Gauss’s theorem for partial integration Z η Z Z Z z=η dx ∇3 Φ · ∇3 (δΦ) dz = − dx [(∇3 · ∇3 Φ)δΦ dz] + dx [(∂N Φ)δΦ]z=−h . −h

Here a boundary term at the lateral boundaries has been neglected. Then the vanishing for all variations δΦ leads to Laplace equation in the interior fluid, the impermeable bottom and the kinematic free surface conditions. The equations are explicitly expressed as ∆3 Φ = 0 for ∇3 Φ · Nb = 0 at

∇3 Φ · Ns = ∂t η at

−h 0. The corresponding kinetic energy is then Z 0 Z 1 ρ2 2 2 (Cu) dx + (Cu) dx. 2g 2g 0 This corresponds to a change of phase speed with a factor ρ and the linear reflection relation is given by 1−ρ . (3.20) R= 1+ρ The calculated reflection from simulation results in the next section will confirm this relation although nonlinear waves show a small deviation from the relation for linear waves.

52

Localization for spatial-spectral implementations

Conversely, if a desired reflection coefficient R is given, the required value of ρ is found from inversion of the explicit relation: ρ=

3.3.2

1−R . 1+R

(3.21)

Frequency dependent reflecting wall

The idea of the previous subsection can now be generalized for frequency or wave length dependent reflection, by multiplying the phase velocity with a quantity ρ (k) resulting in the kinetic energy after the wall as Z 1 2 ˆ K (u, η) = |Cρ u| dx with Cˆρ = ρ (k) C. 2g 0 By prescribing the reflection coefficient depending on frequency ω, 0 ≤ R(ω) ≤ 1, the quantity ρ¯(ω) is given by ρ¯(ω) =

1 − R(ω) . 1 + R(ω)

(3.22)

Then the corresponding quantity ρ depending on the wavenumber k can be obtained by ρ(k) = ρ¯ Ω−1 (3.23) − (ω) with Ω− the dispersion relation at the left, Ω− (k) = kC− (k). In the next section we illustrate this for the case that the longest waves are completely reflected while other wave lengths are reflected only partially; this may serve as a simple model for the complete refection of infragravity waves and partial reflection of shorter waves when coastal waves bounce against a break water.

3.3.3

Run-up on coast

In the modelling of the run-up of waves on a coast, a spatial truncation is applied in the total energy. Then the Hamiltonian is taken to be Z 1 1 2 gη 2 + (Cu) χ dx. (3.24) H(η, u) = 2 g and leads to the nonlinear Hamilton equations 1 ∂t η = − ∂x (C ∗ (Cu.χ)) g 1 ∂t u = −∂x gηχ + Cu. (∂η C) u.χ . g

(3.25)

The simulation interval is changing due to the moving shoreline. The governing dynamic equations (Eq. 3.25) hold on the wet side or active domain of the changing

3.4 Simulation results

53

simulation interval. It turns out that a moving Heaviside function χ(H) can be used to define the wet and dry domain as defined by 0 if H − Hmin < 0 χ(H) = . (3.26) 1 if H − Hmin ≥ 0 Taking χ(H) with H(x, t) = η(x, t) + D(x), Hmin is the minimum total depth that can be simulated depending on the maximal wave number used in the sim2 ulation. The minimum total depth is taken to be Hmin = (ν/kcut ) /g where ν the peak frequency and kcut = max(k)/4. The kcut is motivated in the Fourier method to prevent aliasing as described in [Kurnia and van Groesen, 2014a, van Groesen and van der Kroon, 2012].

3.4

Simulation results

In this section we show the performance of the accurate dispersive models with spatial-spectral implementation in the following inhomogeneous problems: waves over an underwater slope, waves breaking over a bar, breaking waves running up the coast, wave reflection against walls and the dam-break problem. The simulations results of waves over an underwater slope, wave breaking over a bar and the dam-break problem are obtained by the second order model ABHS2 as presented in [Kurnia and van Groesen, 2014a]. The simulation results of breaking waves running up the coast and wave reflection against walls are obtained by the second order equation as presented in this paper. The third and fourth order models ABHS3,4 from [Kurnia and van Groesen, 2014a] give comparable, slightly better, results, at the cost of somewhat larger computation times. Area influxing is used as described in [Lie et al., 2014], and to avoid periodic looping damping zones are employed at both ends of the interval.

3.4.1

Irregular waves running up a slope 0.1 W3

W2

W1

W4 W5

W6

0

bathymetry [m]

−0.1

−0.2

−0.3

−0.4

−0.5

−160

−140

−120

−100

−80

−60

−40

−20

0

20

x [m]

Figure 3.1: Lay out of the experiment of MARINbench 103001 with the location of wave gauges indicated.

54

Localization for spatial-spectral implementations

0.1 0.08 0.06

η [m]

0.04 0.02 0 −0.02 −0.04 −0.06 −0.08 −120

−100

−80

−60 x [m]

−40

−20

0

Figure 3.2: Shown are the spatial wave profiles at (t ≈ 282.5 s) at which an extreme crest height is obtained (red, solid-line), the maximum temporal crest (black, dashed-dot) and the minimum temporal trough (cyan, dots) after 700 s; the bathymetry is shown in a scale of (1:10) (dashed-line, black).

0.08

W6

−0.08 W5

η [m]

0.06

W4

−0.06 W3

0.06 W2

−0.06 200

220

240

260

280

300 time [s]

320

340

360

380

400

Figure 3.3: Elevation time traces at positions W2, x=-94.6 m, W3, x=-69.9 m, W4, x=30 m, W5, x=-24 m, and W6, x=-15.7 m are shown for the measurement (blue, solid-line) and the simulation (red, dashed-line) of MARINbench 103001.

The test case is a wave that after generation travels above a deep area at depth 0.6 m, then runs-up on an uniform slope (1:20) and continues above a flat shallow part with depth 0.3 m. This is a simplified geometry in laboratory scale (spatial factor 50) for the run-up of waves from the deeper sea to the shallower coast. The wave is an irregular wave with spectrum of JONSWAP-type and random phases, with peak period (Tp ) 1.7 s and significant wave height (Hs ) 0.062 m. This wave corresponds to wind waves entering the coastal area with peak period 12 s and significant wave height 3.1 m. The experiment was performed in MARIN (Maritime Research Institute in Netherlands) and registered as MARINbench 103001. Fig. 3.1 shows the lay out of the experiment and location of measurements. For the simulation, the measurement data at W1 is used as influx signal. Simulation results for this case have been presented before in

3.4 Simulation results

55

[van Groesen and van der Kroon, 2012, Adytia and van Groesen, 2012] using BiAB and OVBM equations. Fig. 3.2 shows the spatial wave profile at which an extreme crest is obtained in the approximately 400 wave long wave train. An extreme or freak like wave is usually defined as a wave with wave height more than 2Hs . The freak-like wave is observed at t≈ 282.5 s and at a position close to measurement at W3. Fig. 3.3 shows the time traces of simulations and measurement. The wave shapes are well reproduced during propagation above the deep area (W2, W3), during run-up from the foot of the slope (W4) to the top (W5) and above the flat shallow part (W6). The correlation between simulation and measurement gives quantitative information about the accuracy of the simulation. Deviations from the maximal value 1 of the correlation measures especially the error in phase, a time shift of the simulation; for correlation −1 the simulation is in counter phase with the measurement. In the present simulation, the correlation has been calculated in the time interval (100;700) s at W2, W3, ..., W6 to be 0.95, 0.94, 0.66, 0.90, 0.81. The correlation at W4 gives the lowest value as was also obtained in [van Groesen and van der Kroon, 2012, Adytia and van Groesen, 2012].

3.4.2

Irregular wave breaking over a bar 0.1 0.05 S1

S2

S3 S4 S5 S6

S7

0

bathymetry [m]

−0.05 −0.1 −0.15 −0.2 −0.25 −0.3 −0.35 −0.4

0

5

10

15 x[m]

20

25

30

Figure 3.4: Lay out of the experiments of [Beji and Battjes, 1994], with the location of the wave gauges.

Beji and Battjes [1994, 1993] conducted a series of experiments concerning the propagation of regular and irregular waves over a submerged trapezoidal bar, corresponding to either non-breaking, spilling breaking or plunging breaking waves. In this section we show simulation of an irregular spilling breaking wave, with peak period 1.7 s and significant wave height 0.035 m. Simulations using ABHS2,3 equations for regular wave plunging breaking have been shown in [Kurnia and van Groesen, 2014a]. The bathymetry is presented in Fig. 3.4; the water depth varies from 0.4 m in the deeper region to 0.1 m over the top of the bar. In the experiment the wave height is measured at seven positions: S1, S2, · · · , S7. Position S2 is at the upslope area (a 1:20 slope), positions S3, S4 are at the top of the bar and positions S5, S6 are at the downslope area (a 1:10 slope) and position S7 at the flat bottom close to

56

Localization for spatial-spectral implementations

S7

0.03 S6 −0.03

η [m]

S5

0.04 S4 −0.04 S3

0.04 S2 −0.04 60

70

80

90

100

110

120

130

140

150

time [s]

Figure 3.5: Elevation time traces at positions S2, S3, · · · , S7 are shown for the measurement (blue, solid-line) and the simulation (red, dashed-line) of the irregular breaking wave propagating over a bar.

S7

4 S6 2 0

Amplitude Sp.

S5

5 S4

2 0

S3 6 3 0

S2 0

5

10

ω [rad/s]

15

20

Figure 3.6: Corresponding spectra of the time traces in Fig. 3.5.

the downslope area. The measured surface elevation at S1 at the foot of the slope is used as influx signal for our simulation. In Fig. 3.5 we show the elevation time traces at all measurement positions in the time interval (60; 150) s. The simulated surface elevation is in good agreement with the measurement. The wave transformation, the shoaling process (at S2), breaking at the top of the bar (at S3 and S4) and then the wave decomposition (at S5, S6, S7) are all well reproduced. The main discrepancy between measurement and simulation is observed at the downslope area (S5, S6 and S7). The corresponding spectra are shown in Fig. 3.6. In Fig. 3.7, we show at the top-left the spatial evolution of the maximum tem-

3.4 Simulation results

57

0.05 Hs [m]

MTA [m]

0.06 0.04 0.02

0.04 0.03

0 −0.02 10

11

12

13 x[m]

14

15

16

17

18

Sk

9 −4

x 10

9

10

11

12

13 x[m]

14

15

16

17

18

8

9

10

11

12

13 x[m]

14

15

16

17

18

8

9

10

11

12

13 x[m]

14

15

16

17

18

0 −2

5 1

0

−Asym

MWL [m]

8

2

−5

0 −1

9

10

11

12

13 x[m]

14

15

16

17

Figure 3.7: Spatial evolution of wave characteristics as computed (red, lines) and measured (blue, symbols) of irregular breaking waves propagating over a bar. At the top-left △: maximum temporal crest, ▽: minimum temporal trough, at the bottom-left, ◦: mean water level. At the right, Hs: significant wave height (top), Sk: skewness (middle), As: asymmetry (bottom).

poral crest and the minimum temporal trough (left), at the bottom-left the mean water level; at the right, the significant wave height (top), skewness (middle) and asymmetry (bottom). The skewness Sk measures the crest-trough shape, and the asymmetry As measures the left-right differences in a wave, defined as: Sk =

h(η − η¯)3 i h(η − η¯)2 i3/2

As =

hH(η − η¯)3 i h(η − η¯)2 i3/2

(3.27)

where η¯ is the wave-averaged surface elevation, hi is time averaging operator and H the Hilbert transform. The plots show that the simulation captures the main wave characteristics in a good way.

3.4.3

Harmonic breaking wave running up a coast 0.1 0.05 W2

W1

W3

...

...

W10

W21

0 S2 S3 S4 S5 S6 S7

S1

S8

bathymetry [m]

−0.05 −0.1 −0.15 −0.2 −0.25

1

−0.3

35

−0.35 −0.4 −20

−18

−16

−14

−12

−10 x [m]

−8

−6

−4

−2

0

Figure 3.8: Lay out of the experiments of [Ting and Kirby, 1994]. The location of the wave gauges for surface elevation are indicated by ⋄ (red). The interior horizontal velocity is measured at 8 positions, indicated by ◦ (green), every 0.01 m in the vertical direction.

In this section we show simulation results of a harmonic wave running up a coast. Except for the surface elevation also the interior horizontal velocity is compared to

58

Localization for spatial-spectral implementations

Figure 3.9: Simulation results of breaking waves during run-up; shown are the spatial surface elevation (top), the interior horizontal velocity (middle) and the interior vertical velocity (bottom) at t≈ 60 s. Breaking nodes are indicated by circles (blue).

data of laboratory experiments conducted by Ting and Kirby [1994]. Harmonic waves were generated above a flat bottom with depth 0.4 m and propagate over a 1:35 sloping coast. In this section we show only the spilling breaker case, for which the wave period is T = 2.0 s and the incident wave height H = 0.125 m. The bathymetry is presented in Fig. 3.8, indicating 21 positions of wave elevation measurements and 8 positions of interior horizontal velocity measurements, measured every 0.01 m in the vertical direction. Fig. 3.9 shows results of the simulation: the spatial surface elevation, the interior horizontal velocity and the vertical velocity at t ≈ 60 s. Breaking in the simulation starts at x ≈ −6.9 m which agrees with the measurement, and then continues till the shore. The initiation of breaking in the simulation was obtained by the kinematic criterion U/C >= 0.55 in which U is the crest speed and C is the phase speed at the crest. The corresponding interior horizontal velocity has maximum value in the crest when the breaking starts. Correspondingly, the interior vertical velocity has maximum value in the front of the wave. Fig. 3.10 at the left shows time traces of surface elevation of simulation and measurement at W1 (deep area) to W21 (close to the shore). The wave shape is well reproduced and in phase during shoaling and breaking which takes place at W10. At positions close to shore, the simulation overestimates the wave crest as shown also in the maximum temporal crest plot and skewness plot in Fig. 3.10. However the simulation captures the main wave characteristics in a quite good way. Fig. 3.11 shows the variations of the time-mean horizontal velocity at different depths at several locations indicated in Fig. ¯ √ 3.8. The time-mean horizontal velocity u is normalized by the wave celerity (C = gD). In agreement with the measurement, the calculated time-mean horizontal velocity is in the onshore direction near the surface and in the offshore direction below the trough level. The main discrepancy between the calculated and the measured value is at positions close to the shore.

3.4 Simulation results

W21

0.06 −0.06

W19

0.08 −0.08

W17

0.09 −0.09

W15

0.1 −0.1

W13

0.1 −0.1

W11

0.1 −0.1

W9

0.1 −0.1

W7

0.1

elevation [m]

W18 W16

0.05

0

W14 −0.05

W12 −14

−12

−10

−8 x[m]

−6

−4

−2

W10 0.2 Hs [m]

0.15

W8

0.1 0.05 0

W6

0.09 −0.09

W5

0.08 −0.08

W3

0.08 −0.08

0.15

W20

−14

−12

−10

−8 x[m]

−6

−4

−2

−14

−12

−10

−8 x[m]

−6

−4

−2

−14

−12

−10

−8 x[m]

−6

−4

−2

3 2 Sk

W4

1 0

W2 2

W1 38

40

42

44

46

48 50 time [s]

52

54

56

58

−Asym

η −η ¯ [m]

0.06 −0.06

59

1 0 −1

Figure 3.10: For the harmonic breaking wave running up a coast, at the left the elevation of simulation and experiment as in Fig. 3.5 and at the right same information as in Fig. 3.7.

3.4.4

Wave-wall interactions

In the first subsection we deal with a uniformly partially reflecting wall, i.e. all waves are reflected with the same fraction R. In the second subsection we show results for frequency dependent reflection at the wall. Fully or partially reflecting walls In this section we show simulation of harmonic waves colliding at a fully or partially reflecting wall. The simulation results are compared with analytic solutions. The relation between the reflection coefficient R and the constant ρ in Eq. 3.20 is confirmed by simulation results as shown in Fig. 3.12. The simulation results are for harmonic waves with period 2 s which corresponds to wavelength ≈ 6.3 m, initial wave height 0.1 m, propagating above a flat bottom with depth 5 m and colliding against a wall (at x = 150 m), simulated by the linear Hamilton equations and the second order Hamilton equations for different values of ρ. In Fig. 3.13 we show the spatial wave profile at t = 522.2 s and time trace at

Localization for spatial-spectral implementations

0

S1

0 −0.2 (z − η¯)/D

−0.2 (z − η¯)/D

S2

−0.4 −0.6

S3

0

−0.4

−0.6

−0.8 −0.8

−0.4

−0.4

−0.6

−0.6

−0.8

−0.8

−1

−1 −0.4 −0.2

0 √ u ¯/ gD

0.2

−0.4 −0.2

0.4

0

S5

−0.4 −0.2

0.4

S6

0

0 0.2 √ u¯/ gD

0.4

−0.4 −0.2

0 0.2 √ u¯/ gD

0.4

S8

S7 0

−0.1 −0.2

(z − η¯)/D

−0.4 −0.6

−0.3 −0.4 −0.5

−0.2 (z − η¯)/D

−0.2

−0.2 (z − η¯)/D

0 0.2 √ u¯/ gD

(z − η¯)/D

0

S4

−0.2

−0.2 (z − η¯)/D

0

(z − η¯)/D

60

−0.4

−0.4

−0.6

−0.6

−0.8

−0.8

−0.6 −0.7

−0.8

−0.8 −1

−1 −0.4 −0.2

0 0.2 √ u ¯/ gD

−0.4 −0.2

0.4

0 0.2 √ u ¯/ gD

0.4

−0.4 −0.2

0 0.2 √ u¯/ gD

−0.4 −0.2

0.4

0 0.2 √ u ¯/ gD

0.4

Figure 3.11: Shown are the time-mean horizontal velocity of calculation ◦ (red) and measurement ∗ (blue) below horizontal spatial points S1, S2 · · · , S8 illustrated in Fig. 3.8. 1 0.9 0.8 0.7

R

0.6 0.5 0.4 0.3 0.2 0.1 0

0

0.2

0.4

ρ

0.6

0.8

1

Figure 3.12: Relation between the reflection coefficient R and ρ. Simulation results by the linear Hamilton equations ◦ (red), the nonlinear Hamilton equations ∗ (blue) are compared to the exact relation Eq. 3.20 (solid-line, black).

the wall position x = 150 m of the linear simulation of the harmonic waves with period 2 s. It shown that the reflected wave height is as desired 2 times the initial wave height for full reflection and 1.5 times for 50% reflection. In Fig. 3.14 we show the nonlinear simulations with the same initial wave characteristics. The nonlinear effects lead to a small modulation in the wave elevation. Fig. 3.15 shows linear simulations with different wave periods 4 s and 6 s. The harmonic waves with period 4 s corresponds to wavelength ≈ 22.2 m and period 6 s corresponds to wavelength ≈ 38.1 m. These are long wave compared with the depth of 5 m. The reflected wave height is approximately 2 times the initial wave height for full reflection; the wave with period 6 s shows a slightly higher amplitude at the

3.4 Simulation results

61

0.15

0.15

0.05

η [m]

0.1

0.05

η [m]

0.1

0

0

−0.05

−0.05

−0.1

−0.1 0

20

40

60

80 x [m]

100

120

140

160

0

0.15

0.1 0.05

η [m]

0.1 0.05

η [m]

20

40

60

80 x [m]

520

525 time [s]

100

120

140

160

0.15

0

0

−0.05

−0.05

−0.1

−0.1

500

505

510

515

520

525 time [s]

530

535

540

545

550

500

505

510

515

530

535

540

545

550

Figure 3.13: Reflected harmonic wave profiles at t = 522.2 s (at the top) and time trace at the wall position (at the bottom) for waves with period 2 s with λ/D = 1.3. At the left and at the right are simulation results for 100% and 50% reflecting wall, respectively. Simulations using the linear Hamilton equations are indicate by dashed-line (red), the linear analytic solution by solid-lines (blue), the maximum temporal crest by dashed-dot (black), the minimum temporal trough by dots (cyan) and the wall at x = 150 m by vertical line (yellow) 0.15

0.15

0.05

η [m]

0.1

0.05

η [m]

0.1

0 −0.05

0 −0.05 −0.1

−0.1 0

20

40

60

80 x [m]

100

120

140

0

160

0.1 0.05

η [m]

0.1 0.05

η [m]

20

40

60

80 x [m]

520

525 time [s]

100

120

140

160

0.15

0.15

0

0

−0.05

−0.05

−0.1

−0.1

500

505

510

515

520

525 time [s]

530

535

540

545

500

550

505

510

515

530

535

540

545

550

Figure 3.14: Same as in 3.13. Now for simulations (dashed-line, red) using the the second order Hamilton equations compared to the linear analytic wave (solid-line, blue) 0.15

0.1

0.1

0.05

0.05

η [m]

η [m]

0.15

0 −0.05 −0.1

−0.1 −20

0

20

40

60

80 x [m]

100

120

140

160

180

−50

50

100

150

200

0.15 0.1

0.05

0.05

η [m]

0.1

0 −0.05

0 −0.05

−0.1 500

0

x [m]

0.15

η [m]

0 −0.05

−0.1 505

510

515

520

525 time [s]

530

535

540

545

550

500

505

510

515

520

525 time [s]

530

535

540

545

550

Figure 3.15: Same as in 3.13. Now for simulations with period 4 s (left) and 6 s (right) corresponding to λ/D = 4.4 and 7.6 respectively.

62

Localization for spatial-spectral implementations

wall while small shifts in phase are also observed. Frequency dependent reflecting wall

50

1

1

0

0

0.5

1

ω [rad/s]

1.5

0.5

R and ρ

Amplitude Sp.

0.5

R and ρ

Amplitude Sp.

40

20

0

2

0

0.5

1

ω [rad/s]

1.5

2

0

Figure 3.16: Shown are the spectrum of the influx signal (solid-line, blue), the prescribed reflection coefficient R(ω) (solid-line, green) and the calculated ρ¯(ω) (dashed-dot, green). At the left, ρ¯1 for R1 = 1 − min ω 2 , 0.5 , and at the right, ρ¯2 for R2 = 1 − min ω 2 , 1 .

η [m]

0.1 0 −0.1 0

500

1000

1500

2000

2500

x [m]

η [m]

0.1

0

−0.1 300

400

500

600

700 time [s]

800

900

1000

1100

1200

66.92 0.5

33.46 0

0

0.2

0.4

0.6

0.8 1 ω [rad/s]

1.2

1.4

1.6

Reflection Coef.

Amplitude Sp.

200

0

Figure 3.17: Shown are simulation results with the reflection coefficient R1 (blue, solidline), R2 (green, dashed-line) and without wall (red, dashed-dot). At the top, the wave profiles at time t = 1000 s and maximum temporal amplitudes for: simulation with the wall (black, solid-line for R1 and cyan, dashed-line for R1 ), without wall (magenta, dashed-dot) and the wall at x = 2500 m (yellow, vertical line). The middle plot shows time traces at the wall position. The bottom plot shows the spectrum at the wall position with at the left axis the amplitude spectra, and at the right axis the value of the reflection.

In this section we show simulation results of waves colliding at a frequency dependent reflecting wall. The waves are irregular waves with JONSWAP spectrum with gamma 3.3, significant wave height 0.1 m, peak period 12 s above a flat bottom with depth 25 m. We show comparison of the second order nonlinear simulationwith and without wall, for walls with two reflection properties R1 = 1 − min ω 2 , 0.5 and R2 = 1 − min ω 2 , 1 as shown in Fig. 3.16.

3.4 Simulation results

63

Fig. 3.17 shows that with R1 the simulation shows the correct full reflection of long waves and partial reflection R ∈ [0.5, 1) for shorter waves. With R2 the simulation shows partial reflection with R ∈ (0, 1] for ω < 1, and full transmission of shorter waves.

3.4.5

Dam-break problem

0.15 1

0

t1

t2

t3

t4

t5

t6

η/h

η/h0

0.1 t7

0.05

0.5 t*=10

0 0

20

40 x/h0

0.4

60

0 0

80

t*=24

t*=48 t*=62

50

100

t*=95 150

x/h

0

0

η/h

η/h0

1 0.2 t1 0 0

t2 20

t3

t4 40 x/h

t5

t6

0.5

t7

60

t*=10 0 0

80

t*=24 t*=32

t*=95 150

1

0.6

0

0.4

η/h

η/h0

100 x/h0

0

0.5 t*=10

0.2 t1 0 0

t*=62

50

t2 20

t3

t4

40 x/h

0

t5 60

t6

t7 80

0 0

t*=24 50

t*=40

t*=62 100

t*=95 150

x/h

0

Figure 3.18: At the left are shown spatial surface elevations for undular bore simulations with initial height (η/h0 ) 0.1 (top), 0.2 (middle), 0.3 (bottom) at various times: t1 = 10, t2 = 20, t3 = 30, · · · , t7 = 70. At the right are shown the elevations for breaking bore simulations with initial height 0.43 (top), 0.52 (middle), 0.6 (bottom); the breaking nodes are indicated by ◦ (blue).

In this section we simulate undular bores propagating into constant-depth, still water. This case is also known as the dam break problem that has been widely studied as a standard illustration of competing effects of dispersion and nonlinearity. In this testcase we reproduced and extended simulations of previous work by Wei et al. [1995]. The initial conditions describe a gentle transition between a uniform flow and still water 1 1 η = u + u2 . (3.28) u = u0 [1 − tanh(x/a)] , 2 4 Here η is the surface elevation and u is the velocity. In our models the velocity is the tangential velocity, which is different from the horizontal velocity in [Wei et al., 1995]. u0 is the velocity of the uniform flow from the left boundary and a is a number sufficiently large so that the initial motion can be described by Airy’s theory. The same value a = 5 is used and u0 is chosen so that the surface elevation at the left boundary is as required η0 = 0.1, 0.2, 0.3. The simulations as shown in Fig. 3.18 at the p left are presented in the same scale as in Fig. 7 of [Wei et al., 1995], t∗ = t/ h0 /g, x∗ = x/h0 with h0 = 1. Qualitatively the simulations using the Hamilton equations are similar with the simulations using the fully nonlinear potential flow presented in Fig. 7 [Wei et al., 1995].

64

Localization for spatial-spectral implementations

To simulate more extreme cases, we increased the initial surface elevation to values η0 = 0.43; 0.52; 0.6 that lead to breaking bores, shown in Fig. 3.18 at the right. The bores start to break at time t∗ = 24, 32 and 40 at different positions for the simulations with three different initial conditions respectively. The waves are shown to break at the front.

3.5

Conclusion

It is quite remarkable that the method proposed here, the rather straightforward generalization given in Eq. 3.12 of the explicit expression of the phase velocity from Airy’s linear theory, leads to a model and implementation that performs so well for even the most difficult cases as shown in Section 3.4. A major reason must be that the model has the exact asymptotic behaviour of the limit of linear waves above flat bottom, as well as the shallow water limit, both limits valid for all types of waves i.e. for all wave lengths; this despite the strict conclusion about the second order accuracy from the classical ’order’ reasoning as presented in Section 3.2.3 which may be too pessimistic for the model that is inherently based on a non-algebraic formulation. Provided the Fourier Integral Operators are correctly dealt with, in particular the symmetry properties, the Hamilton equations are obtained in a very explicit way. Consequently, the actual numerical implementation is very simple: using FFT’s for the spatial discretization and an explicit time solver, the explicit formulas are literally copied without any adjustments or ’trics’. For computational effectiveness, the interpolation of the symbols in the FIO’s is essential; in all cases considered so far (including those in this paper), just 2 or 3 interpolants are enough to get accurate results. As a consequence, most simulations can be done in (essentially) less than 25% of the physical time in environmental geometries. With the methods described in this paper in Section 3.3 we have overcome the localization problems that are typical for global methods such as Fourier methods. At this moment similar methods are used to model and simulate wave-ship interactions, results of which will be published elsewhere. Although the simulations are performed in a dimension reduced way, the calculation of the internal flow as described in Section 3.2.5 will be useful for various applications. Simulations as shown in this paper can be performed with HAWASSI-AB software.

Chapter

4

Design of wave breaking experiments and a-posteriori simulations 1 Summary In this chapter, we present results of 30 wave breaking experiments that were designed by HAWASSI-AB software. The experiments were carried out in a wave tank of Technical University of Delft (TUD). The use of the efficient simulation code can optimize the experiments by designing the influx such that waves will break at a predefined position. The consecutive actual measurements agree well with the numerical design of the experiments. Using the measured elevation close by the wave maker as input, the software recovers the experimental data in great detail, even for rather short (up to L/D=1) and very steep breaking waves with steepness parameter (ak) till 0.4.

4.1

Introduction

For the design of fixed or flexible structures in the coastal area such as wind mills and oil platforms, knowledge of expected forces in extreme waves are of paramount importance. Experiments in wave tanks are often used to obtain impact data in well-controlled circumstances. Since the interest is mainly in extreme wave conditions, it is required to prepare the incoming wave such that the desired extreme behaviour takes place at the defined position of the structure. Limitations on the wave generator and the complicated distortions during the wave propagation towards the structure makes this a challenging task. 1 The contents of the chapter is partly presented as a proceeding article [Kurnia et al., 2015] and an internal report [Kurnia and van Groesen, 2015a]

66

Design of wave breaking experiments and a-posteriori simulations

This chapter presents results of 30 wave breaking experiments conducted in the long wave tank of TU Delft, Department of Maritime and Transport Technology (6,7 and 10-12 March 2014). Simulations performed before the experiment to determine the required wave maker motion and a-posteriori simulations that use a measured time trace as influx for calculation further downstream are also presented. The 30 different experiments cover a broad range of breaking waves of various types. Those are roughly grouped together as follows: 11 focussing waves, 7 bichromatic wave trains, 9 irregular waves, 2 cases of ’soliton on finite background’, 1 harmonic wave with added focussing wave. Characteristic for all cases is the rather broad spectrum (although restricted by wave maker properties). In each group, the cases differ in amplitude, period and steepness. The range of wavelength for these cases runs from 1 to 4 times the depth and the steepness parameter (ak) till 0.4. 27 experiments showed breaking as designed; the harmonic focussing case, and the two test cases TUD1403Ir7 and TUD1403Foc12 were (designed to be) non-breaking. The aim of this Chapter is to show that HAWASSI-AB, a Hamiltonian Boussinesq model with breaking mechanism, is sufficiently accurate to support the design task prior to the actual experiment. Moreover, the a-posteriori use of the measured elevation close to the wave maker to initiate the simulation, leads to reconstruction of the waves that is accurate at all measurement positions. The organization of this chapter is as follows. Section 4.2 describes the laboratory experimental set-up. Section 4.3 gives a brief description of the simulation model. In Section 4.4, comparison of measurement results with the a-priori and a-posteriori simulation will be presented. Conclusions will finish this chapter.

4.2

Experimental set up

The wave tank at Technical University of Delft was used to perform the experiments. The tank is 142 m long, 4.22 m wide and the depth during the experiment was 2.13 m. At the end of the tank, waves are absorbed by an artificial beach. Waves are generated by a flap type wavemaker. Fig. 4.1 shows a cross-section of the wave tank. Resistance type of wave probes were used to measure surface elevation at various positions at the centre-line of the tank. The wave probes operate by measuring the current that flows between two stainless steel wires that are immersed in the water. This current is converted to an output voltage that is directly proportional to the immersed depth. Calibration of a potentiometer on the wavemaker and the wave probes in the fluid has been done before the start of the experiments. This calibration has been used to determine the transfer function for optimized performance. The same measurement positions were used for a total of 30 different experiments. The experiments were designed in such a way that most breaking waves could be caught at the same position, which then were selected as the measurement positions. The position of breaking of the waves did not always coincide precisely with the wave probe positions. Nevertheless, from the recorded video and markers in

4.3 Simulation model

67

Figure 4.1: The wave tank of TUD. View from a carriage at approximately 70 m to wave maker.

the wavetank, the breaking position and breaking moment could be approximated afterwards. Comparison of observed and simulated breaking events will be shown in the next section on design and reconstruction. A schematic lay-out is shown in Figure 4.2. The elevation is measured at positions W1 at x = 10.31 m, W2 at x = 40.57 m, W3 at x = 60.83 m, W4 at x = 65.57 m, W5 at x = 70.31 m and W6 at x = 100.57 m.

Figure 4.2: Layout of the experimental set-up.

In Appendix A.1 an overview of the experiments is given with all main wave parameters.

4.3

Simulation model

The model used for the numerical simulations is part of HAWASSI-AB, the Hamiltonian Wave Ship-Structure Interaction, using Analytic Boussinesq model. For the present cases only the wave facility has been used. A full description of the code and the breaking model can be found in [Kurnia and van Groesen, 2014a]. The most characteristic properties of the model are now summarized. The model is of Boussinesq type, which means that the interior fluid motion is not calculated but modelled so that a spatial reduction is obtained. The model has a Hamiltonian structure, with main consequence that it is exactly energy conserving for non-breaking waves.

68

Design of wave breaking experiments and a-posteriori simulations

The main disadvantage of most Boussinesq equations is overcome by using a spatial-spectral implementation so that dispersion is exact for all wave lengths in the order of nonlinearity of the equation. For the experiments in this chapter, the third-order equation (ABHS3 in [Kurnia and van Groesen, 2014a]) has been used. Wave generation is done in an embedded way by influxing the given elevation signal at the influx position through a source in the continuity equation; in [Lie, 2013] this generation is described in detail. Here area influxing has been used with an adaptation area to prevent the generation of spurious waves for the extreme influx heights used in some of the experiments. For breaking the mechanism as proposed by Kurnia and van Groesen [2014a] is used; the initiation of breaking is determined by a kinematic breaking criterion. Instead of the absorbing beach of the wave tank, the simulated wave is smoothly damped to avoid any reflections from the end. Simulations with the HAWASSI-AB code are reasonably fast; depending on the specific case, computation times are 0.5 to less than 3 times the physical time. The simulations are also robust for change of parameters such as grid size, initiation of breaking, etc. as shown in [Kurnia and van Groesen, 2014a].

4.4

Design and reconstruction

Of the 30 experiments listed in Appendix A.1 we select a few characteristic cases for presentation here. A full account of all simulations is available in Appendix A.2 and A.3. In the first subsection we compare measurement results with the a-priori simulated wave; we call this the design case. It will be seen that there are some discrepancies between the designed waves and the experiments, but the differences are for most practical applications acceptable. In the second subsection we compare the measurements with the simulated waves that use the measured elevation at W1 as input for simulation; we call this the reconstruction. These simulation results compare better with the experiments. This indicates that the transfer function used to translate information from the designed waves to the wave maker motion must account for the differences. In all cases, the waves were approximated with an analytic model choosing the steepness parameters such that breaking could be expected. Then the simulation using HAWASSI-AB gave a complete overview of the designed waves including the positions of breaking. In the following plots of wave elevations, measurements are indicated by blue (solid) lines, and simulations by red (dashed) lines.

4.4.1

Design cases

To determine input for the wavemaker, the elevations signal at 10 m of the a-priori simulated wave has been taken. Using the transfer function of the the wavemaker, the actual wavemaker motion has been calculated. The range of frequencies for the

4.4 Design and reconstruction

69

input of the wave maker is (2.4, 6) [rad/s] which restricts the generation of waves to periods in between 1 s and 2.6 s. We now describe the results for two cases. Experiment TUD1403Foc7 is a focussing wave often used in laboratories to generate very high waves as an effect of dispersive wave focussing, in this case with an amplification of about 2.73. As shown in Figure 4.3, qualitatively the agreement between design and experiment is good, but differences in the spectra further downstream are quite noticeable at higher frequencies. The breaking position in the design is 65 m and the observed breaking in the experiment takes place at 59 m. The wave was designed to break at the focussing position but in the experiment the wave breaks one peak wavelength before the focussing. 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1

W1

W6 1 0.5

W5

W4 S ||S inf lux ||∞

η[m]

0

1 0.5 0 W2 1 0.5

40

W3

50

60

70

80

90 t[s]

100 110 120 130

0 0

W1 1

2

3

4 5 ω [rad/s]

6

7

8

Figure 4.3: Elevation time traces (left) and normalized spectra (right) of TUD1403Foc7 at positions W1, · · · , W6 are shown for the measurement (blue, solid) and for the simulation (red, dashed dot).

Experiment TUD1403Bi3 is a bichromatic wave; for specific parameters see Appendix A.1. Severe breaking takes place at multiple positions. Figure 4.4 shows plots of wave elevations and spectra. The spectrum shows substantial energy loss due to breaking; spectra and time traces at different positions show a gradual down-shift of the bi-chromatic pattern, with higher order waves developing and disappearing further downstream. The spectrum of design and experiment agree quite well; the time traces at larger distances differ in the small wave separation regions between the wave groups. Figure 4.5 shows the positions and times of breaking in the simulation (solid dots, red). Breaking in the experiment as observed in reality and in a movie is indicated also (open dots, blue) but the observation of breaking events in the experiment is limited from x ≈ 50 m to x ≈ 70 m.

70

Design of wave breaking experiments and a-posteriori simulations

0.1 W6 0 −0.1

W6 1

0.1 W5 0 −0.1

0.5 0

W4 S ||S inf lux ||∞

η[m]

0.1 W4 0 −0.1 0.1 W3 0 −0.1 0.1 W2 0 −0.1

1 0.5

W3

0 W2 1

0.1 W1 0 −0.1 40

W5

0.5

60

80

100 120 t[s]

140

160

180

0 0

W1 1

2

3

4 5 ω [rad/s]

6

7

8

Figure 4.4: Same as Fig. 4.3. Now for TUD1403Bi3. 120 110

Breaking position [m]

100 90 80 70 60 50 40 30 20 40

60

80

100 time [s]

120

140

160

Figure 4.5: Wave breaking positions of TUD1403Bi3 for the simulation (red, solid dots) and the observation in reality and in a movie (blue, open dots).

4.4.2

Reconstruction cases

We now reconstruct the experiments by taking the measured elevation at W1 as input signal for the numerical code. Experiment TUD1403Foc7 This focussing wave with ka ≈ 0.11 shows single wave breaking. The elevation time traces and the spectra are well reconstructed as shown in Figure 4.6. The differences in the spectra further downstream are rather small. The wave breaks at x = 59.2 m in the simulation and at x ≈ 59.5 in the experiment. Experiment TUD1403Ir10 This irregular wave with ka ≈ 0.27 shows successive wave breaking for a few waves. During propagation the spectrum becomes slowly broader, with limited energy decay. The spectra and time traces comparisons are shown in Figure 4.7 and the breaking positions in Figure 4.8.

4.5 Conclusions

71

Experiment TUD1403Bi3 This bichromatic wave shows abundant continued wave breaking of the steep waves with ka ≈ 0.3. The elevation time traces and the spectra are well reconstructed as shown in Figure 4.9. Observe the substantial down-shift in the spectrum which may be caused by the breaking, and the substantial energy dissipation. The breaking position of simulation and the limited observation are shown in Figure 4.10.

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

1 0.5

W6

W5

S ||S inf lux ||∞

η[m]

0

1 0.5

W4

0

60

W3

1 0.5

70

80

90

100 t[s]

110

120

130

140

0 0

W2

1

2

3

4 5 ω [rad/s]

6

7

8

Figure 4.6: Same as Fig. 4.3. Now for reconstruction.

4.5

Conclusions

The use of an accurate numerical code can optimize the experiments. A comparison of the design simulations prior to the experiment and the measurements show that the time traces at the measurement positions are quite accurate; the substantial changes in the measured spectra at the successive positions compare reasonably well with the changes of the prior design simulations. However, there are some discrepancies between the designed waves and the corresponding experiments. In the focussing wave case (TUD1403Foc7), the actual breaking position takes place one peak wavelength in front of the designed position, but the focussing position is the same as designed a priori. Taking the actual experimental wave elevation time trace at the first measurement point as input for the simulations for reconstruction a posteriori the experiment, both breaking and focussing positions of simulation and measurement are in good agreement. This indicates that the transfer function used to translate information from the designed waves to the wave maker accounts for the differences that were observed in the design cases.

Design of wave breaking experiments and a-posteriori simulations

0.2 0 −0.2 0.2

η[m]

0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0

1

W6

0.5

W6

0

W5

W5

S ||S inf lux ||∞

72

W4

1 0.5

W4

0

W3

W3

1

W2

0.5

−0.2 40

60

80

100

120

140

160

180

200

W2

0 0

220

1

2

3

t[s]

4 5 ω [rad/s]

6

7

8

Figure 4.7: Same as Fig. 4.3. Now for TUD1403Ir10 (reconstruction). 120 110

Breaking position [m]

100 90 80 70 60 50 40 30 20 100

150

200

250

time [s]

Figure 4.8: Same as Fig. 4.5. Now for TUD1403Ir10 (reconstruction).

The irregular wave case (TUD1403Ir10) showed successive wave breaking for a few waves leading to broadening of the spectrum during propagation with limited energy decay. The simulations showed quantitatively good correlations with measurements. The bichromatic wave case (TUD1403Bi3), showed abundant continued wave breaking of the steep waves leading to the substantial down-shift in the spectrum and the substantial energy decay. In Table 4.1, we show the correlations at all measurement positions and the relative computation time (Crel). The correlation between the time traces of the measurement and the simulation is defined as the inner product between the normalized signals. Deviations from the maximal value 1 of the correlation measures especially the error in phase, a time shift of the simulation; for correlation -1 the simulation is in counter phase with the measurement. The relative computation time is defined as the cpu-time divided by the total time of the simulation; the calculations

4.5 Conclusions

73

1

0.1 W6 0 −0.1

0.5

W6

0 W5

S ||S inf lux ||∞

η[m]

0.1 W5 0 −0.1 0.1 W4 0 −0.1

1 0.5

W4

0

0.1 W3 0 −0.1

W3

1

0.1 W2 0 −0.1 60

0.5

80

100

120

140

160

W2

0 0

180

1

2

3

t[s]

4 5 ω [rad/s]

6

7

8

Figure 4.9: Same as Fig. 4.3. Now for TUD1403Bi3 (reconstruction). 120 110

Breaking position [m]

100 90 80 70 60 50 40 30 20

60

80

100

120 time [s]

140

160

180

Figure 4.10: Same as Fig. 4.5. Now for reconstruction.

were performed on a desktop computer with CPU i7, 3.4 GHz processor with 16 GB memory. The simulations show quantitatively good correlations in phase with measurements; and the calculation times rather short.

74

Design of wave breaking experiments and a-posteriori simulations

Table 4.1: Correlations at measurement positions for the various test cases between simulations and measurements. D stands for the design cases (experiment after simulation) and R for the reconstruction. Crel is the relative computation time.

W1 W2 W3 W4 W5 W6 Crel

TUD1403Foc7 D R 0.93 0.91 0.99 0.88 0.97 0.87 0.98 0.89 0.98 0.92 0.97 1.14 1.13

TUD1403Ir10 D R 0.94 0.92 0.97 0.85 0.96 0.84 0.95 0.86 0.94 0.81 0.86 2.48 2.43

TUD1403Bi3 D R 0.97 0.86 0.96 0.74 0.90 0.68 0.87 0.67 0.84 0.63 0.78 1.83 3.2

Chapter

5

Conclusions and recommendations 5.1

Conclusions

In this dissertation various aspects of water wave modelling are considered. The main topic is the development of an accurate and efficient model that can simulate wave propagation in any range of wave lengths and in any water depth. Moreover, it is desired that the model can deal with various inhomogeneous problems such as bathymetry and walls, leading to wave structure interactions. A challenge in the study of water waves is that the motion can exhibit qualitative differences at different scales such as deep water versus shallow water, long wavelength versus short wavelength, etc.. That leads to a restriction in the applicability of the existing wave models. It is remarkable that the accurate dispersive wave models, the AB (Analytic Boussinesq) models as presented in this dissertation, showed outstanding performance in terms of efficiency and accuracy. The AB models are uniformly valid for any depth, for large amplitudes and have wide applicability. A major reason is that the AB models were derived consistently from the Hamiltonian formulation. The approximated Hamilton equations were expressed in the exact phase speed operators with correct order of non-linearity in wave elevation. Thanks to the spatial-spectral implementation the exact dispersion property can be retained without any approximation. The dispersion is essential to obtain highquality wave propagation results. This improves the properties of more classical Boussinesq type of equations. The Hamiltonian consistent approximation guarantees correct evolution of momentum and (approximated) energy. Furthermore, the AB models can deal with various difficult cases such as breaking or non breaking waves that propagate over a submerged bar or a slope, run-up on the coast, with presence of partially or fully reflective walls, including the dam-break problem. To deal with breaking waves, an extended eddy viscosity breaking model that is applicable for fully dispersive waves was implemented. A kinematic breaking

76

Conclusions and recommendations

criterion that the wave will break when the horizontal particle speed exceeds (a fraction of) the crest speed was used as a trigger mechanism. To deal with localized effects i.e walls, coasts, submerged bar, etc., a localization method was applied in the global Fourier integral operators that are associated with the nonlinear phase speed operator. It is known that Fourier expansion techniques, different from finite difference or finite element method, lead to some problem when complicated geometric structures need to be included. The inclusion of such fixed structures in a spatial-spectral setting has been shown in this dissertation, it serves perhaps as a first contribution in this topic. In many applications such as the calculation of wave force on structures requires information of interior properties. A method to calculate or recover the internal flow in the time dynamic or post-processing step of the Boussinesq model has also been shown in this dissertation. An extensive comparison with (at least 50) laboratory data has been performed. The previous Chapter presented the 30 measurement data of wave breaking experiments in TUD wave tank that were designed using the AB models. It was shown that an efficient and accurate code can optimize wave-tank experiments. Simulations as shown in this dissertation can be performed with HAWASSI-AB software. The demo version can be downloaded on http://hawassi.labmath-indonesia.org.

5.2

Recommendations

For further research the following outlook is given: • In Chapter 3 a generalized AB model was derived. It has been indicated that the model has second order accuracy from the classical order reasoning. This can be improved by starting the derivation from the anzatz of nonlinear extension of the Airy potential and then substituted into the kinetic energy. • In Chapter 2 the kinematic criterion requires that the wave will break when the horizontal particle speed exceeds (a fraction of) the crest speed. A universal value of this parameter is not known yet. Further investigations on the breaking criterion are much desired. • The present models aim to simulate long crested waves. The simulation of short crested waves is expected to be a straightforward extension to two horizontal dimensions. • The method to model wave interactions with fixed structures has been presented. An extension to deal with floating structures such as ships can be done in the future. A Hamiltonian formulation of wave-ship interaction has been derived recently by van Groesen and Andonowati [2015].

Appendix

A

Supplementary files of the experiments This Appendix provides information of the wave breaking experiments that were presented in Chapter 4. The characteristic quantities of all main wave parameters are presented in Section A.1. The comparison between the experiments and apriori simulations is presented in Section A.2. The full comparison between the experiments and a-posteriori simulations is presented in Section A.3.

A.1

The characteristic quantities of the designed waves

The following table summarises the characteristic quantities of all the designed waves. The successive columns provide the following information: t max: maximum time, Tp: peak period, (T 0, dt): T 1 = T 0 + dt/2, T 2 = T 0 − dt/2 (Bichromatic periods), λp: peak wavelength, kp.a: steepness, H0: maximum wave height of influx signal, MTT: maximum temporal trough, MTC: maximum temporal crest, H1: maximum wave height of maximal signal, H1/H0: amplification, xb: successive breaking positions (separated by semicolon), or the range of breaking position as indication of many breaking events (denoted by x1-x2), and tb: the corresponding breaking time. The information is based on a-priori simulations.

78

Supplementary files of the experiments

A.2 Comparison of experiments and a-priori simulations

A.2

79

Comparison of experiments and a-priori simulations

η[m]

Bichromatic wave: TUD1403Bi3 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1

W1

40

60

80

100 t[s]

120

140

160

180

120

W6 110

1

100

0.5

Breaking position [m]

W5

0

S ||S influx ||∞

W4 1 W3

0.5 0

W2

90 80 70 60 50 40

1 W1

0.5 0 0

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 40

60

80

100 time [s]

120

140

Figure A.1: Elevation time traces (top) and normalized amplitude spectra (left below) at positions W1, W2, W3, W4, W5, and W6 are shown for the measurement (blue, solid) and for the design simulation with model ABHS3 (red, dashed dot). At the right below, the positions of breaking of the design simulation (red, solid dots) and the limited observation (x ∈ (50, 70)) in reality (in the movie, blue, open dots).

Table A.1: Wave properties: period, peak wavelength, steepness. Correlation at W1-W6 and relative computation time (Crel).

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.3

W1 0.97

W2 0.86

W3 0.75

W4 0.68

W5 0.67

W6 0.63

Crel 1.83

160

80

Supplementary files of the experiments

η[m]

Irregular wave: TUD1403Ir10

0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 40

W6

W5

W4

W3

W2

W1 60

80

100

120

140

160

180

200

t[s] 120

W6 110

1

100

W5 Breaking position [m]

0.5 0

S ||S influx ||∞

W4 1 0.5

W3

0 W2

90 80 70 60 50 40

1 0.5 0 0

W1

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 40

60

80

100

120 140 time [s]

160

Figure A.2: Same as Fig. A.1. Now for TUD1403Ir10.

Table A.2: Same as Table A.1. Now for TUD1403Ir10.

Tp 1.96

λp 5.87

kp .a 0.24

W1 0.94

W2 0.92

W3 0.85

W4 0.84

W5 0.86

W6 0.81

Crel 1.87

180

200

220

A.2 Comparison of experiments and a-priori simulations

81

η[m]

Focussing wave: TUD1403Foc7 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1

W1

40

50

60

70

80

90

100

110

120

130

t[s] 120

W6 110

1

100

W5 Breaking position [m]

0.5 0

S ||S influx ||∞

W4 1 0.5

W3

0 W2

90 80 70 60 50 40

1 0.5 0 0

W1

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 40

60

80

100

120 140 time [s]

160

Figure A.3: Same as Fig. A.1. Now for TUD1403Foc7 case.

Table A.3: Same as Table A.1. Now for TUD1403Foc7 case.

Tp 1.96

λp 5.89

kp .a 0.11

W1 0.93

W2 0.91

W3 0.88

W4 0.87

W5 0.88

W6 0.92

Crel 1.5

180

200

220

82

Supplementary files of the experiments

A.3

Comparison of experiments and a-posteriori simulations

η[m]

Focussing wave group: TUD1403Foc1

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

2

4

ω [rad/s]

6

8

10

20 20

40

60

80

100

120 140 time [s]

160

180

200

Figure A.4: Elevation time traces (top) and normalized amplitude spectra (left below) at positions W2, W3, W4, W5, and W6 are shown for the measurement (blue, solid) and for the a-posteriori simulation with model ABHS3 (red, dashed dot). At the right below, the positions of breaking of the design simulation (red, solid dots) and the limited observation (x ∈ (50, 70)) in reality (in the movie, blue, open dots).

Table A.4: Wave properties: peak period, peak wavelength, steepness. Correlation at W2-W6 and relative computation time (Crel).

Tp 1.85

λp 5.3

kp .a 0.19

W2 0.98

W3 0.97

W4 0.96

W5 0.96

W6 0.97

Crel 1.35

220

A.3 Comparison of experiments and a-posteriori simulations

83

η[m]

Focussing wave group: TUD1403Foc2

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

50

60

70

80 t[s]

90

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

110

120

1 0.5

100

W2

30

2

4

ω [rad/s]

6

8

10

20 20

40

60

80

100

120 140 time [s]

Figure A.5: Same as Fig. A.4, now for TUD1403Foc2 case.

Table A.5: Same as Table A.4. Now for TUD1403Foc2 case.

Tp 1.7

λp 4.46

kp .a 0.16

W2 0.98

W3 0.94

W4 0.94

W5 0.94

W6 0.88

Crel 0.68

160

180

200

220

84

Supplementary files of the experiments

Focussing wave group: TUD1403Foc5

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

50

60

70

80

90

100

110

120

t[s] 120

1 0.5

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

80 70 60 50 40

1 0.5

90

W2

1

30

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.6: Same as Fig. A.4, now for TUD1403Foc5 case.

Table A.6: Same as Table A.4. Now for TUD1403Foc5 case.

Tp 1.92

λp 5.7

kp .a 0.21

W2 0.96

W3 0.96

W4 0.96

W5 0.94

W6 0.93

Crel 0.92

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

85

Focussing wave group: TUD1403Foc6

0.2

W6

0 −0.2 0.2

W5

0

η[m]

−0.2 0.2

W4

0 −0.2 0.2

W3

0 −0.2 0.2

W2

0 −0.2 70

80

90

100 t[s]

110

W6

100 Breaking position [m]

S ||S influx ||∞

W5

1 W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

140

110

0

0.5

130

120

1 0.5

120

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.7: Same as Fig. A.4, now for TUD1403Foc6 case.

Table A.7: Same as Table A.4. Now for TUD1403Foc6 case.

Tp 1.89

λp 5.52

kp .a 0.12

W2 0.99

W3 0.96

W4 0.95

W5 0.96

W6 0.95

Crel 1.06

160

180

200

220

86

Supplementary files of the experiments

η[m]

Focussing wave group: TUD1403Foc7

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

70

80

90

100 t[s]

110

W6

100 Breaking position [m]

S ||S influx ||∞

W5

1 W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

140

110

0

0.5

130

120

1 0.5

120

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.8: Same as Fig. A.4, now for TUD1403Foc7 case.

Table A.8: Same as Table A.4. Now for TUD1403Foc7 case.

Tp 1.96

λp 5.89

kp .a 0.11

W2 0.99

W3 0.97

W4 0.98

W5 0.98

W6 0.97

Crel 1.13

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

87

η[m]

Focussing wave group: TUD1403Foc8

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

70

80

90

100 t[s]

110

W6

100 Breaking position [m]

S ||S influx ||∞

W5

1 W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

140

110

0

0.5

130

120

1 0.5

120

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.9: Same as Fig. A.4, now for TUD1403Foc8 case.

Table A.9: Same as Table A.4. Now for TUD1403Foc8 case.

Tp 1.96

λp 5.89

kp .a 0.13

W2 0.99

W3 0.97

W4 0.97

W5 0.97

W6 0.97

Crel 0.56

160

180

200

220

88

Supplementary files of the experiments

Focussing wave group: TUD1403Foc9

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.10: Same as Fig. A.4, now for TUD1403Foc9 case.

Table A.10: Same as Table A.4. Now for TUD1403Foc9 case.

Tp 2.16

λp 6.96

kp .a 0.17

W2 0.99

W3 0.96

W4 0.96

W5 0.96

W6 0.96

Crel 1.17

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

89

Focussing wave group: TUD1403Foc10

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.11: Same as Fig. A.4, now for TUD1403Foc10 case.

Table A.11: Same as Table A.4. Now for TUD1403Foc10 case.

Tp 2.2

λp 7.2

kp .a 0.13

W2 0.99

W3 0.97

W4 0.97

W5 0.98

W6 0.97

Crel 1.08

160

180

200

220

90

Supplementary files of the experiments

Focussing wave group: TUD1403Foc11

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.12: Same as Fig. A.4, now for TUD1403Foc11 case.

Table A.12: Same as Table A.4. Now for TUD1403Foc11 case.

Tp 2.2

λp 7.2

kp .a 0.16

W2 0.99

W3 0.97

W4 0.98

W5 0.98

W6 0.98

Crel 1.21

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

91

Focussing wave group: TUD1403Foc12 (non breaking)

W6

0.1 0 −0.1

W5

0.1 0

η[m]

−0.1 W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1 60

70

80

90

100 t[s]

1

2

3

4 ω [rad/s]

110

120

130

140

7

8

1 0.5

W6

0

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5

W2

0 0

5

6

Figure A.13: Same as Fig. A.4, now for TUD1403Foc12 case.

Table A.13: Same as Table A.4. Now for TUD1403Foc12 case.

Tp 2.38

λp 8.26

kp .a 0.06

W2 0.97

W3 0.96

W4 0.97

W5 0.97

W6 0.97

Crel 1.70

92

Supplementary files of the experiments

Focussing wave group: TUD1403Foc13

0.2

W5

0 −0.2

η[m]

0.2

W4

0 −0.2 0.2

W3

0 −0.2 0.2

W2

0 −0.2 60

70

80

90

100 t[s]

110

120

130

140

120

W5

110

Breaking position [m]

S ||S influx ||∞

100

1 W4 0.5 0 W3

1

80 70 60 50 40

W2 0.5 0 0

90

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.14: Same as Fig. A.4, now for TUD1403Foc13 case.

Table A.14: Same as Table A.4. Now for TUD1403Foc13 case.

Tp 2.4

λp 8.25

kp .a 0.14

W2 0.98

W3 0.96

W4 0.95

W5 0.96

Crel 2.44

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

93

η[m]

Bichromatic wave: TUD1403Bi2

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120

140

160

180

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.15: Same as Fig. A.4, now for TUD1403Bi2 case.

Table A.15: Same as Table A.4. Now for TUD1403Bi2 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.20

W2 0.93

W3 0.88

W4 0.86

W5 0.83

W6 0.67

Crel 2.3

160

180

200

220

94

Supplementary files of the experiments

η[m]

Bichromatic wave: TUD1403Bi3

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120

140

160

180

t[s] 120

1 0.5

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

80 70 60 50 40

1 0.5

90

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20

60

80

100

120 time [s]

Figure A.16: Same as Fig. A.4, now for TUD1403Bi3 case.

Table A.16: Same as Table A.4. Now for TUD1403Bi3 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.3

W2 0.96

W3 0.90

W4 0.87

W5 0.84

W6 0.78

Crel 3.2

140

160

180

A.3 Comparison of experiments and a-posteriori simulations

95

Bichromatic wave: TUD1403Bi4

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 60

80

100

120

140 t[s]

160

200

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.17: Same as Fig. A.4, now for TUD1403Bi4 case

Table A.17: Same as Table A.4. Now for TUD1403Bi4 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.36

W2 0.93

W3 0.82

W4 0.79

W5 0.75

W6 0.63

Crel 3.6

160

180

200

220

96

Supplementary files of the experiments

η[m]

Bichromatic wave: TUD1403Bi6

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120 t[s]

140

180

140

1 0.5

160

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.18: Same as Fig. A.4, now for TUD1403Bi6 case

Table A.18: Same as Table A.4. Now for TUD1403Bi6 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.18

W2 0.98

W3 0.94

W4 0.92

W5 0.90

W6 0.86

Crel 1.9

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

97

Bichromatic wave: TUD1403Bi7

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 50

100

150

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.19: Same as Fig. A.4, now for TUD1403Bi7 case

Table A.19: Same as Table A.4. Now for TUD1403Bi7 case.

(T0,dt) (1.7,0.06)

λp 4.3

kp .a 0.29

W2 0.98

W3 0.97

W4 0.96

W5 0.95

W6 0.92

Crel 1.4

160

180

200

220

98

Supplementary files of the experiments

Bichromatic wave: TUD1403Bi8

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.20: Same as Fig. A.4, now for TUD1403Bi8 case.

Table A.20: Same as Table A.4. Now for TUD1403Bi8 case.

(T0,dt) (1.6,0.06)

λp 3.82

kp .a 0.33

W2 0.96

W3 0.93

W4 0.93

W5 0.91

W6 0.81

Crel 2.3

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

99

Bichromatic wave: TUD1403Bi9

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 60

80

100

120 t[s]

140

180

140

1 0.5

160

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.21: Same as Fig. A.4, now for TUD1403Bi9 case.

Table A.21: Same as Table A.4. Now for TUD1403Bi9 case.

(T0,dt) (1.5,0.06)

λp 3.38

kp .a 0.37

W2 0.95

W3 0.93

W4 0.91

W5 0.88

W6 0.79

Crel 3.7

160

180

200

220

100

Supplementary files of the experiments

η[m]

Irregular wave: TUD1403Ir1

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

50

100

150

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.22: Same as Fig. A.4, now for TUD1403Ir1 case.

Table A.22: Same as Table A.4. Now for TUD1403Ir1 case.

Tp 1.4

λp 3.14

kp .a 0.25

W2 0.95

W3 0.92

W4 0.91

W5 0.88

W6 0.89

Crel 7.5

200

A.3 Comparison of experiments and a-posteriori simulations

101

Irregular wave: TUD1403Ir2

0.1 W6 0 −0.1

η[m]

0.1 W5 0 −0.1 0.1 W4 0 −0.1 0.1 W3 0 −0.1 0.1 W2 0 −0.1 60

80

100

120

140 t[s]

160

180

200

220

1 0.5

W6 120

0

Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

100

80

60

40

1 0.5 0 0

W2 20

2

4

ω [rad/s]

6

8

50

10

100

150 time [s]

Figure A.23: Same as Fig. A.4, now for TUD1403Ir2 case.

Table A.23: Same as Table A.4. Now for TUD1403Ir2 case.

Tp 1.32

λp 2.74

kp .a 0.28

W2 0.91

W3 0.82

W4 0.80

W5 0.79

W6 0.66

Crel 11

200

102

Supplementary files of the experiments

Irregular wave: TUD1403Ir3

0.1 W6 0 −0.1 0.1 W5 0 −0.1

η[m]

0.1 W4 0 −0.1 0.1 W3 0 −0.1 0.1 W2 0 −0.1 60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

2

4

ω [rad/s]

6

8

10

20

50

100

150 time [s]

Figure A.24: Same as Fig. A.4, now for TUD1403Ir3 case.

Table A.24: Same as Table A.4. Now for TUD1403Ir3 case.

Tp 1.28

λp 2.57

kp .a 0.34

W2 0.77

W3 0.61

W4 0.61

W5 0.58

W6 0.53

Crel 8.1

200

A.3 Comparison of experiments and a-posteriori simulations

103

Irregular wave: TUD1403Ir4

0.2

W6

0 −0.2 0.2

W5

0

η[m]

−0.2 0.2

W4

0 −0.2 0.2

W3

0 −0.2 0.2

W2

0 −0.2 40

60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.25: Same as Fig. A.4, now for TUD1403Ir4 case.

Table A.25: Same as Table A.4. Now for TUD1403Ir4 case.

Tp 1.63

λp 4.18

kp .a 0.27

W2 0.97

W3 0.96

W4 0.96

W5 0.96

W6 0.92

Crel 1.2

200

104

Supplementary files of the experiments

η[m]

Irregular wave: TUD1403Ir7 (non breaking)

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

40

60

80

100

120 t[s]

140

160

180

200

1 0.5

W6

0

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5

W2

0 0

2

4

6 ω [rad/s]

8

10

Figure A.26: Same as Fig. A.4, now for TUD1403Ir7 case.

Table A.26: Same as Table A.4. Now for TUD1403Ir7 case.

Tp 2.6

λp 9.4

kp .a 0.15

W2 0.96

W3 0.97

W4 0.96

W5 0.96

W6 0.93

Crel 0.54

12

A.3 Comparison of experiments and a-posteriori simulations

105

Irregular wave: TUD1403Ir8

0.2 0 −0.2

η[m]

0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2

W6

W5

W4

W3

W2

40

60

80

100

120

140 t[s]

160

200

220

240

100

150

200

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

2

4

6 ω [rad/s]

8

10

12

20

50

time [s]

Figure A.27: Same as Fig. A.4, now for TUD1403Ir8 case.

Table A.27: Same as Table A.4. Now for TUD1403Ir8 case.

Tp 1.96

λp 5.87

kp .a 0.24

W2 0.97

W3 0.97

W4 0.97

W5 0.96

W6 0.95

Crel 1.7

106

Supplementary files of the experiments

Irregular wave: TUD1403Ir9

0.2 W5 0 −0.2 0.2

η[m]

W4 0 −0.2 0.2 W3 0 −0.2 0.2 W2 0 −0.2 40

60

80

100

120 t[s]

140

160

180

200

120

W5

110

Breaking position [m]

S ||S influx ||∞

100

1 W4 0.5 0 W3

1

80 70 60 50 40

W2 0.5 0 0

90

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

160

180

200

Figure A.28: Same as Fig. A.4, now for TUD1403Ir9 case. Info about breaking in experiment missing.

Table A.28: Same as Table A.4. Now for TUD1403Ir9 case.

Tp 1.96

λp 5.87

kp .a 0.24

W2 0.98

W3 0.97

W4 0.96

W5 0.96

Crel 1.87

220

A.3 Comparison of experiments and a-posteriori simulations

107

Irregular wave: TUD1403Ir10

0.2 0 −0.2 0.2

η[m]

0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0

W6

W5

W4

W3

W2

−0.2 40

60

80

100

120

140

160

180

200

220

t[s]

120

1 0.5

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

80 70 60 50 40

1 0.5

90

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 100

150

200 time [s]

Figure A.29: Same as Fig. A.4, now for TUD1403Ir10 case.

Table A.29: Same as Table A.4. Now for TUD1403Ir10 case.

Tp 1.8

λp 5.02

kp .a 0.27

W2 0.97

W3 0.96

W4 0.95

W5 0.94

W6 0.86

Crel 1.11

250

108

Supplementary files of the experiments

Irregular wave: TUD1403Ir11

0.2 0 −0.2

η[m]

0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2

W6

W5

W4

W3

W2

60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

160

180

200

Figure A.30: Same as Fig. A.4, now for TUD1403Ir11 case. Info about breaking in experiment missing.

Table A.30: Same as Table A.4. Now for TUD1403Ir11 case.

Tp 2.08

λp 6.55

kp .a 0.23

W2 0.97

W3 0.96

W4 0.96

W5 0.95

W6 0.94

Crel 1.8

220

A.3 Comparison of experiments and a-posteriori simulations

109

Soliton on Finite Background: TUD1403SFB1

0.1

W6

0 −0.1 0.1

W5

0 −0.1

η[m]

0.1

W4

0 −0.1 0.1

W3

0 −0.1 0.1

W2

0 −0.1 60

80

100

120

140

160

180

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.31: Same as Fig. A.4, now for TUD1403SFB1 case.

Table A.31: Same as Table A.4. Now for TUD1403SFB1 case.

Tp 1.3

λp 2.65

kp .a 0.17

W2 0.98

W3 0.88

W4 0.89

W5 0.89

W6 0.77

Crel 1.9

200

110

Supplementary files of the experiments

η[m]

Soliton on Finite Background: TUD1403SFB2

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

40

60

80

100

120 t[s]

140

180

200

140

1 0.5

160

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.32: Same as Fig. A.4, now for TUD1403SFB2 case.

Table A.32: Same as Table A.4. Now for TUD1403SFB2 case.

Tp 1.5

λp 3.53

kp .a 0.26

W2 0.97

W3 0.91

W4 0.91

W5 0.89

W6 0.88

Crel 3.2

200

A.3 Comparison of experiments and a-posteriori simulations

111

η[m]

Harmonic focussing: TUD1403HF2 (non breaking) 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120

140

160

t[s]

1 0.5

W6

0

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5

W2

0 0

1

2

3

4 ω [rad/s]

5

6

7

Figure A.33: Same as Fig. A.4, now for TUD1403HF2 case.

Table A.33: Same as Table A.4. Now for TUD1403HF2 case.

Tp 2.29

λp 7.7

kp .a 0.14

W2 0.99

W3 0.97

W4 0.97

W5 0.97

W6 0.97

Crel 2.2

8

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Acknowledgments

The research presented in this dissertation has been carried out over the past 4 years in the Applied Analysis (AA) group, Department of Applied Mathematics, University of Twente (UT). It is largely inspired and encouraged by my supervisor, family, friends and colleagues whom I would like to acknowledge. First and foremost, I would like to express sincere gratitude to my supervisor, Prof. E. (Brenny) van Groesen, who I am indebted to for many things. I met Brenny for the first time when I applied an internship position at LabMath-Indonesia (LMI) in June 2011. At that time, i was finishing my master thesis. After I graduated, He offered me a position to pursue PhD degree at University of Twente and never thought before that the opportunity would bring me this far. I am thankful to him for the attentive guidance, fruitful discussions and the continuous support. His significant role helped me in finishing this dissertation. Again, I am grateful to him for giving me an opportunity to work as a post-doctoral researcher at UT and LMI starting from 1 February 2016. I would like to pronounce my sincere thanks to Prof. Stephan van Gils, the chair of AA group, for the opportunity to work in his group, and also his willingness to be one of my graduation committee. I would also like to thank other members of my graduation committee: Prof. Frederic Dias, Prof. Rene Huijsmans, Prof. Arthur Veldman, Prof. Bayu Jayawardhana, and Dr. Tim Bunnik for agreeing in the committee and for reviewing my thesis. I would also thank Prof. Peter Apers as the chairperson and the secretary of my graduation committee. I would also like to express my gratitude to Prof. Rene Huijsmans for giving me an excellent opportunity to conduct the wave breaking experiments in a wave tank at Technical University of Delft. All support during the experiments from his group member: Peter Poot, Peter Naaijen and Toni van den Munckhof are greatly appreciated. I thank MARIN for the use of the data, and in particular Dr. Tim Bunnik for discussions about the results and the organisation of the meetings. I wish to express my thanks to Dr. Andonowati for providing me a nice research atmosphere during short visits at LMI. In LMI, I met many people with whom I can discuss about everything. I thank Didit, Andreas, Hafizh, Liam, Mourice, Meirita,

Andy, Nugrahinggil, Abrari, Lia, Januar, Lawrance and others. Many friends and colleagues in the Department of Applied Mathematics have shown a great help to my academic life at campus. A special word of thanks goes to the secretaries Marielle and Linda for all the administrative arrangements. I thank Gerard Jeurnink for involving me in educational activities. Thanks to everyone who I have shared my office with: Arnida, Anastasia, Elena, Devashish, Jurgen, Leonie, Freekjan. I would also like to thank the other members of the group: Huan, Lulu, Deepak, Edo, Bettina, Edson, Felix, Wilbert, Tatyana, and others. I am really grateful for being surrounded by many warmhearted people during my stay in Enschede. I thank tante Soefiyati Hardjosumarto and Inggrid Proost for their kindness and for countless invitation to their house. I wish to express my thanks to Erwin vonk, Esther, Wisnu, Wenny, and Nida. I am also very thankful to all member of Indonesian Student Association in Enschede (PPIE) whom I cannot name one by one, which made my stay in Enschede enjoyable. I am grateful to my family especially my sisters: Chiely, Inalia and Dian for their support. I am truly grateful to my parents, Handreas Syamdiputra and Herliana Taniman for their unconditional love, prayer and support. Finally, I thank my wife, Erika Tivarini for her love and support. Above all, I thank God for His grace and guidance in my life.

About the author

Ruddy Kurnia was born on the 1th of May 1987 in Bandung, Indonesia. He obtained a degree of Bachelor of Science from Physics department of Institut Teknologi Bandung (ITB), Indonesia in July 2009 on a subject of electromagnetic method for geophysics exploration. In August 2009, he started his Master’s study on double degree program of computational science at Kanazawa University, Japan and Institut Teknologi Bandung, Indonesia. He finished his study in August 2011, on a subject of particle methods for computational fluid dynamics. From June 2011 to January 2012, he worked as an internship student at LabmathIndonesia on a subject of water wave modelling. In February 2012, he started his Ph.D research in Applied Analysis group, Department of Applied Mathematics, University of Twente. After 4 years, he finished his doctoral study which the result of his research is presented in this dissertation. Starting from 1 February 2016, he works as a post-doctoral researcher at University of Twente and Labmath-Indonesia. In this project, he is extending the applicability of the HAWASSI software.

Ruddy Kurnia

Samenstelling promotiecommissie: Voorzitter en secretaris: prof. dr. P. M. G. Apers

University of Twente

Promotor prof. dr. ir. E. W. C. van Groesen

University of Twente

Leden prof. dr. S. A. van Gils prof. dr. A. E. P. Veldman prof. dr. ir. R. H. M. Huijsmans prof. dr. F. Dias prof. dr. B. Jayawardhana dr. ir. T. Bunnik

University of Twente University of Twente Delft University of Technology University College Dublin, Ireland University of Groningen MARIN

The research presented in this dissertation was carried out at the Applied Analysis group, Departement of Applied Mathematics, Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) of the University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organisation for Scientific Research (NWO) and partly funded by the Ministry of Economic Affairs (project number 11642).

c 2016, Ruddy Kurnia, Enschede, The Netherlands Copyright Cover: Erika Tivarini, www.erikativarini.carbonmade.com Printed by Gildeprint, Enschede isbn 978-90-365-4039-1 doi 10.3990/1.9789036540391 http://dx.doi.org/10.3990/1.9789036540391

HAWASSI-AB MODELLING AND SIMULATION OF FULLY DISPERSIVE NONLINEAR WAVES ABOVE BATHYMETRY

DISSERTATION

to obtain the degree of doctor at the University of Twente, on the authority of the rector magnificus, prof. dr. H. Brinksma, on account of the decision of the graduation committee, to be publicly defended on Friday 19 February 2016 at 16:45

by

Ruddy Kurnia born on the 1th of May 1987 in Bandung, Indonesia

Dit proefschrift is goedgekeurd door de promotor prof. dr. ir. E. W. C. van Groesen

To my parents

Summary

Water waves propagating from the deep ocean to the coast show large changes in the profile, wave speed, wave length, wave height and direction. The fascinating processes of the physical wave phenomena give challenges in the study of water waves. The motion can exhibit qualitative differences at different scales such as deep water versus shallow water, long waves versus short waves. Therefore, the existing mathematical models are restricted to the limiting cases. This dissertation concerns the development of an accurate and efficient model that can simulate wave propagation in any range of wave lengths, in any water depth and moreover can deal with various inhomogeneous problems such as bathymetry and walls, leading to wave structure interactions. The derivation of the model is based on a variational principle of water waves. The resulting dynamic equations are of Hamiltonian form for wave elevation and surface potential with non-local operators applied to the canonical surface variables. The Hamiltonian is the total energy, i.e the sum of kinetic energy and potential energy. Since the kinetic energy cannot be expressed explicitly in the basic variables an approximation is required. The corresponding approximated Hamiltonian leads to approximated Hamilton equations. The approximate Hamilton equations are expressed in pseudo-differential operators applied to the surface variables. The pseudo-differential operator has a physical interpretation related to the phase velocity. The phase velocity as function of wave length is specified by a dispersion relation. Dispersion is one of the most important physical properties in the description of water waves. Accurate modelling of dispersion is essential to obtain high-quality wave propagation results. Using spatial-spectral methods and a straightforward numerical implementation, accurate and fast performance of the model can be obtained. Moreover, the spatialspectral implementation with the global pseudo-differential operators or a generalization with global Fourier integral operators (FIO) can retain the exact dispersion property of the model. Other numerical implementations with local differential operators such as finite difference or finite element methods require that the dispersion is approximated by an algebraic function. Such an approximation leads to restrictions on the range of wave lengths that are modelled correctly. To deal with practical applications, several extensions of the model are imple-

viii mented. The model with localization methods in the global FIO can deal with localized effects such as breaking waves, partially or fully reflective walls, submerged bars, run-up on shores, etc. The inclusion of a fixed-structure in the spatial-spectral setting is a challenging task. The method as presented here perhaps serves as a first contribution in this topic. An extended eddy viscosity breaking model and a breaking kinematic criterion are used for the wave breaking mechanism. The extended eddy viscosity breaking model can deal with fully dispersive waves. The kinematic breaking criterion prescribes that a wave will break when the horizontal particle speed exceeds (a fraction of) the crest speed. A universal or deterministic value of this parameter is not known yet. In many applications, such as the calculation of wave forces on structures, requires information of interior flow properties. A method to calculate the interior flows in a post-processing step of the Boussinesq model is described. Performance of the model is shown by comparing the simulation result with measurement data of various long crested cases of breaking and non-breaking waves. The model has been extensively tested against at least 50 measurement data. Moreover, 30 measurement data of wave breaking experiments were designed by the accurate wave model. It will be shown that an efficient and accurate code can optimize the experiments. The models and methods presented in this dissertation have been packaged as software under the name HAWASSI-AB; here HAWASSI stands for Hamiltonian Wave-Ship-Structure Interaction, while AB stands for Analytic Boussinesq. More information of the software can be found on http://hawassi.labmath-indonesia.org.

Samenvatting

Watergolven vertonen gedurende hun reis van de diepe oceaan naar de ondiepe kust grote veranderingen in vorm, snelheid, golflengte en richting. De fascinerende processen van deze fysische golfverschijnselen leiden tot uitdagend onderzoek. De beweging kan leiden tot kwalitatieve verschillen op verschillende schalen van waterdiepte en golflengte. Daarom zijn veel wiskundige modellen beperkt tot limiet gevallen. Dit proefschrift behandelt het ontwikkelen van een nauwkeurig en efficint model dat de voortplanting kan beschrijven en berekenen van golven met willekeurige golflengte boven willekeurige waterdiepte, zelfs in interactie met inhomogeniteiten zoals veranderende bodemdiepte of de aanwezigheid van wanden. De afleiding van het model is gebaseerd op een variatieprincipe voor watergolven. De resulterende dynamische vergelijkingen zijn een Hamiltons systeem voor de golfhoogte en de oppervlakte potentiaal met niet-lokale operatoren die werken op deze canonieke oppervlakte variabelen. De Hamiltoniaan is de totale energie, de som van kinetische en potentiele energie. Omdat de kinetische energie niet expliciet uitgedrukt kan worden in de basisgrootheden is een benadering vereist. De daarmee corresponderende Hamiltoniaan leidt tot de benaderde Hamilton vergelijkingen. Deze vergelijkingen zijn uitdrukkingen met pseudo-differentiaal operatoren toegepast op de oppervlakte variabelen. Deze operator is fysisch gerelateerd aan de fase-snelheid. Deze snelheid wordt bepaald door de golflengte via de zogenaamde dispersie-relatie. Dispersie is een van de meest belangrijke eigenschappen in de beschrijving van watergolven, en een goede benadering is essentieel om goede resultaten te verkrijgen voor golfvoortplanting. Ruimtelijk-spectrale methoden en een directe numerieke implementatie leiden tot nauwkeurige en snelle resultaten. Bovendien kan door de ruimtelijk-spectrale implementatie van de globale pseudo-differentiaal operatoren, of de generalisatie naar Fourier integraal operatoren (FIO), de exacte dispersie-eigenschappen van het model bewaard worden. Overige numerieke implementaties met lokale differentiaal operatoren, zoals eindige-differentie of eindige-element methoden, vereisen een benadering van de dispersie met een algebrasche functie, hetgeen tot beperkingen leidt van de golflengten die nauwkeurig voortgeplant worden. Om praktische problemen aan te kunnen pakken zijn meerdere uitbreidingen geimplementeerd. Localisatie-methoden voor de globale FIOs maken het mogelijk

x gelocaliseerde effecten te simuleren, zoals brekende golven, gedeeltelijk of volledig reflecterende wanden, onderwaterdrempel, oploop op de kust, etc. Dit toevoegen van vaste structuren in ruimtelijk-spectrale modellen is een uitdagende taak; de bijdragen daaraan die hier worden gepresenteerd zijn misschien de eersten van dit soort. Een eddy-viscositeits breking model met een kinematisch breking criterium worden gebruikt voor golfbreking; het brekingmodel is uitgebreid zodat het bruikbaar is voor volledig dispersieve golven. Het kinematisch criterium zorgt ervoor dat een golf breekt als de horizontale deeltjessnelheid groter is dan een fractie van de snelheid van de golftop. Een universele of deterministische waarde voor die fractie is nog niet bekend. In veel toepassingen zijn de interne stromingssnelheden van belang, bijvoorbeeld voor de berekening van krachten op structuren. Er wordt een methode gepresenteerd om de interne stroming te berekenen nadat de oppervlaktegrootheden van het Boussinesq model zijn berekend. De prestaties van het model zijn aangetoond voor meer dan 50 gevallen door berekende resultaten te vergelijken met meetdata van experimenten van langkammige golven met of zonder breking. Bovendien zijn met de software 30 experimenten van golfbreking ontworpen, waarmee aangetoond wordt dat daarmee het experimenteren geoptimaliseerd kan worden. Het model inclusief alle nieuwe methoden is als software beschikbaar onder de naam HAWASSI-AB. De afkorting HAWASSI staat voor Hamiltonian Wave-ShipStructure Interaction, en AB voor Analytic Boussinesq; meer informatie is te verkrijgen op http://hawassi.labmath-indonesia.org.

Contents

Summary

vii

Samenvatting 1 Introduction 1.1 A historical note on the study of water 1.2 Variational water wave modelling . . . 1.3 Contributions in this dissertation . . . 1.4 Outline of the dissertation . . . . . . .

ix

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1 3 6 9 11

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13 14 15 16 17 20 21 21 23 25 26 27 27 28 28 36 41

3 Localization for spatial-spectral implementations 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Spatial-spectral modelling within the Hamiltonian structure . . . . .

43 44 45

waves . . . . . . . . . . . .

. . . .

. . . .

. . . .

2 High order Hamiltonian water wave models 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 2.2 Variational wave description . . . . . . . . . . . . . 2.2.1 Hamiltonian formulation . . . . . . . . . . . 2.2.2 Consistent approximations . . . . . . . . . . 2.2.3 Hybrid Spatial Spectral implementation . . 2.3 Wave-breaking model . . . . . . . . . . . . . . . . . 2.3.1 Eddy-viscosity model . . . . . . . . . . . . . 2.3.2 Kinematic breaking criterion . . . . . . . . 2.3.3 Alternative viscosity model . . . . . . . . . 2.4 Numerical implementation . . . . . . . . . . . . . . 2.4.1 Damping zones . . . . . . . . . . . . . . . . 2.4.2 Nonlinear wave generation . . . . . . . . . . 2.5 Simulation results . . . . . . . . . . . . . . . . . . 2.5.1 Irregular wave breaking over a flat bottom . 2.5.2 Wave breaking over a bar . . . . . . . . . . 2.6 Conclusion and remarks . . . . . . . . . . . . . . .

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xii

CONTENTS

3.3

3.4

3.5

3.2.1 Hamiltonian structure . . . . . . . . . . . . . . . . . . . 3.2.2 Limiting cases . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Second order accurate approximation above bathymetry 3.2.4 Wave breaking and bottom friction . . . . . . . . . . . . 3.2.5 Internal flow and pressure . . . . . . . . . . . . . . . . . Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Partially reflecting wall . . . . . . . . . . . . . . . . . . 3.3.2 Frequency dependent reflecting wall . . . . . . . . . . . 3.3.3 Run-up on coast . . . . . . . . . . . . . . . . . . . . . . Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Irregular waves running up a slope . . . . . . . . . . . . 3.4.2 Irregular wave breaking over a bar . . . . . . . . . . . . 3.4.3 Harmonic breaking wave running up a coast . . . . . . . 3.4.4 Wave-wall interactions . . . . . . . . . . . . . . . . . . . 3.4.5 Dam-break problem . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Design of wave breaking experiments and 4.1 Introduction . . . . . . . . . . . . . . . . . 4.2 Experimental set up . . . . . . . . . . . . 4.3 Simulation model . . . . . . . . . . . . . . 4.4 Design and reconstruction . . . . . . . . . 4.4.1 Design cases . . . . . . . . . . . . 4.4.2 Reconstruction cases . . . . . . . . 4.5 Conclusions . . . . . . . . . . . . . . . . .

a-posteriori . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46 47 48 49 50 51 51 52 52 53 53 55 57 59 63 64 65 65 66 67 68 68 70 71

5 Conclusions and recommendations 5.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . .

75 75 76

Appendix A Supplementary files of the experiments A.1 The characteristic quantities of the designed waves . . . . . . . . . . A.2 Comparison of experiments and a-priori simulations . . . . . . . . . A.3 Comparison of experiments and a-posteriori simulations . . . . . . .

77 77 79 82

Bibliography

113

Acknowledgments

119

About the author

121

Chapter

1

Introduction

Figure 1.1: The Great Wave off Kanagawa, by Katushika Hokusai (18th century) (source: www.wikipedia.org)

Ocean waves are fascinating. The wind blowing over the sea surface generates wind waves. During storms, waves can become very high and develop foamy crests with very complex patterns. Waves approaching the shore get higher and steeper and may break to form waves that are spectacularly used by surfers. The breaking of large oceanic waves has drawn the most attention of human beings to observe this magnificent phenomenon. These natural processes have repeatedly been the themes in paintings. The Great Wave off Kanagawa (Fig. 1.1) is a well-known paintings, published in 18th century by Katsushika Hokusai. The wave has been discussed in scientific notes of [Cartwright and Nakamura, 2009, Dudley et al., 2013]. It is stated that the location of the wave is estimated to be 3 km offshore Tokyo Bay. The estimated wave height of around 10 m leads to the conclusion that this would be a wave of exceptionally large amplitude for this area and would likely be a rogue

2

Introduction

or freak wave. No less important are the scientific studies or concept of the wave phenomena and the ocean as well. For thousands of years, people have been depending on the ocean as a source of food and mineral, and as relatively easy medium for transport of people and goods. Nowadays, with developing of knowledge and technology, the ocean gives even more benefits. Resources of renewable energy such as wind farms, tidal and wave energy are mainly located in coastal areas. Moreover, coastal areas are centres of industrial activities, products and therefore money flows into countries through ports. This leads to the fact that half of the world population lives less than 150 km from the coast.

Figure 1.2: At the left: a photo taken on January 5, 2005 of the devastated district of Banda Aceh, Indonesia in the aftermath of the December 26, 2004 tsunami. Credit: Choo Youn-Kong/AFP/Getty Images. Source: theatlantic.com. At the right: Tsunami wave approaches Miyako city in Japan on 11 March 2011. Credit: Mainichi Shimbun /Reuters. Source: reuters.com.

Figure 1.3: At the left: A rogue wave reaching a height of 18 m hit a tanker headed south from Valdez, Alaska in February 1993. Credit: Captain Roger Wilson, NOAA National Weather Service Collection. At the right: The surface elevation time history recorded at the Draupner platform, which includes the New Year Wave. Source: [Adcock et al., 2011].

Apart from the profits, waves can also give problems. High waves during storms or caused by bathymetry or by collision against constructions or by undersea earthquakes can do great harm to ships, constructions and to people living near the coast.

1.1 A historical note on the study of water waves

3

On 26 December 2004, a Mw 9.1 undersea megathrust earthquake at the west coast of northern Sumatra, Indonesia generated a series of devastating tsunamis along the coasts of the Indian ocean. The series of waves reached the coasts of Banda Aceh (northwest corner of Sumatra) within 15 min after the earthquake, thus inundating 100 km2 of land. The waves were 5-30 m high at the coast and runup to 51 m and 6 km inland [Paris et al., 2007]. The reported number of casualties were approximately 230.000 killed in Indonesia, at least 29,000 killed in Sri Lanka, more than 10,000 in India, more than 5,000 in Thailand, and 82 killed in Maldives, and more than 22,000 are still missing [Kawata et al., 2005]. On 11 March 2011, a Mw 9.0 earthquake in the Pacific ocean close to Tohoku generated tsunami waves. The waves inundated the area with wave heights up to 15 m, runup height reached over 39 m and 6 km inland. Over 14.000 people were reported as dead and over 11.000 were missing [Mimura et al., 2011]. Furthermore, extreme waves, also known as rogue waves or freak waves, have been major causes of numerous accidents of oil-platforms and ships. Practically, a rogue wave is expected to be at least twice larger than the significant wave height. In February 1993, a rogue wave in the Gulf of Alaska was photographed by Captain Roger Wilson [Wilson, 1993]. The wave was reaching a height of 18 m above 7.6 m water depth. The rogue wave hit a tank ship on the starboard side when the ship was heading to south from Valdez, Alaska. On 1 January 1995, the ”New Year wave” was recorded in the North Sea at the Statoil-operated ”Draupner” platform [Adcock et al., 2011]. The Draupner wave was the first rogue wave to be detected by a measuring instrument. It was recorded that the crest height was 18.6 m, wave height 25.6 m above 70 m water depth. Fortunately this wave did not cause substantial damage, but attracted attention of the scientists to this problem. Since then, numerous accidents of oil-platforms and ships have been linked to the rogue wave occurrence. Nikolkina and Didenkulova [2011] collected evidence of rogue wave existence during the 5 year period, 2006-2010. From the total of 131 reported events, 78 were identified as evidence of rogue waves. Only events associated with damage and human loss were included. It is also stated that the extreme waves cause more damage in shallow waters and at the coast than in the deep sea. Therefore, a sustainable and safe development of the oceanic and coastal areas is of paramount importance. The fascination and the practical relevance have been motivating extensive study of water waves, probably as long as people live on earth but certainly in the past centuries. The past and recent studies of water waves are summarized in the following sections. Section 1.1 summarizes the extensive study in the past centuries, and Section 1.2 gives a description of variational water wave modelling. Highlights of the contributions of this dissertation are presented in Section 1.3. The outline of the dissertation will finish this chapter.

1.1

A historical note on the study of water waves

The water wave problem in fluid mechanics has been known since more than three hundreds years [Craik, 2004]. In 1687, Isaac Newton attempted a theory of water

4

Introduction

waves with an analogy of a fluid oscillations in a U-shaped tube. He correctly deduced that the frequency of deep-water waves must be proportional to the inverse of the square root of the breadth of the wave. In 1757, Leonhard Euler published a physically and mathematically successful description of the behaviour of an idealized fluid (inviscid flow). These Euler equations represent conservation of mass (continuity) and momentum. The Euler equations became the foundation of a realistic description of water which was derived 65 years later by Claude Navier. That is now known as the Navier-Stokes equations. Pierre-Simon Laplace (1776) derived a fundamental equation of tidal motion. He focused on free surface propagation, which only occurs if the cause of the wave is localized in space and time. This leads to the general initial value problem: Given any localized initial disturbance of the liquid surface, what is the subsequent motion? Cauchy and Poisson later addressed this problem. Later, Joseph Louis Lagrange (1781) also worked on the governing equation of linear water waves and obtained the solution in the limiting case of shallow water. He found that the speed of propagation of waves will be independent of wavelength and proportional to the square root of water depth; that is (gh)1/2 where g is the gravitational acceleration and h the water depth. In December 1813, the French Acad´emie des Sciences announced a mathematical prize competition on wave propagation on infinite depth. In 1816 Cauchy won the prize and his work was published in 1827. Independently, Poisson, who was one of the judges, deposited a memoir of his own work that was published in 1818. The Cauchy-Poisson analysis is now acknowledged as an important milestone in the mathematical theory of initial-value problem. Cauchy employed Fourier transform in analysing the Laplace equation for the velocity potential Φ(x, y, z) with x, y the horizontal coordinates and z the vertical coordinate ∂2Φ ∂2Φ ∂2Φ + + =0 ∂x2 ∂y 2 ∂z 2

(1.1)

incorporating the linearized free surface condition, with g the acceleration of gravity, ∂2Φ ∂Φ +g = 0. 2 ∂t ∂z

(1.2)

Cauchy then takes the second time-derivative of Eq. 1.2 as 2 ∂3Φ ∂3Φ ∂4Φ 2∂ Φ = −g = g . = −g ∂t4 ∂t2 ∂z ∂z∂t2 ∂z 2

Using Eq. 1.1 Cauchy’s equation is given by 2 ∂4Φ ∂ Φ ∂2Φ = 0. + g + ∂t4 ∂x2 ∂y 2

(1.3)

(1.4)

For a periodic wave of form exp[i(kx x + ky y − ωt)], the correct dispersion relation of deep-water waves can be obtained as ω 2 = g(kx2 + ky2 )1/2 .

1.1 A historical note on the study of water waves

5

However, Cauchy’s equation is only valid in the case of infinite depth since the bottom condition is neglected. In 1834, solitons, waves that propagate with constant speed and constant shape, were observed for the first time by the British scientist John Scott Russell. He was watching a barge being towed along a canal between Glasgow and Edinburg. On its sudden stop, a wave was observed, that propagated for nearly a mile with only little change of form. This phenomenon inspired him to perform experiments. Substantial reports by Russell and Robinson were published in 1837 and 1840. Russell wrote a brief supplementary report (1842) and then his major ”Report on Waves” (1844). Later, Boussinesq in 1872, and Korteweg and de Vries in 1895 produced theoretical results of the soliton wave. In 1841, George Biddel Airy published an influential article ’Tides and Waves’. His work became a major contribution of water wave theory. He gave a complete formulation of linear propagation of gravity waves. In his formulation, an impermeable boundary-condition was taken into account. The formulation is given as follows ∂2Φ ∂2Φ ∂2Φ + + = 0 for − h ≤ z ≤ 0 (1.5) ∂x2 ∂y 2 ∂z 2 ∂Φ + gη = 0 for z = 0 (1.6) ∂t ∂Φ ∂η = for z = 0 (1.7) ∂t ∂z ∂Φ = 0 for z = −h (1.8) ∂z in which Φ is the fluid potential, η the surface elevation, h the water depth and g the gravity acceleration. Airy’s equations represent incompressible and irrotational flow in the interior (Eq. 1.5), a dynamic free surface condition (Eq. 1.6), a kinematic free surface condition (Eq. 1.7) and an impermeable bottom condition (Eq. 1.8). Observe that the free surface conditions are actually the Cauchy condition (Eq. 1.2). Airy’s linear theory produces a correct dispersion relation for a propagating q monochromatic wave, η(x, y, t) = a cos(kx x+ky y −ωt) with a the amplitude, k = kx2 + ky2 the wave number and ω the angular frequency. The dispersion relation of wave propagation above a depth h is given by ω 2 = gk tanh(kh).

(1.9)

The dispersion relation also tells that the wave speed (which is the quotient of ω and k) depends on wavelength. As a consequence, the shorter waves travels slower. The work of Airy on the linear wave theory and the remarkable experiments of Russel motivated Stokes to investigate the water wave problem. In 1847, Stokes published his work on nonlinear wave theory that is accurate up to third order in wave steepness (k.a). He showed surface elevation η in a plane wavetrain on deep water could be expanded in powers of the amplitude a as 3 1 η(x, t) = a cos(kx − ωt) + ka cos 2(kx − ωt) + (ka)2 cos 3(kx − ωt) + · · · 2 8

6

Introduction

where ω 2 = gk 1 + (ka)2 + · · · the nonlinear dispersion. As a consequence of the nonlinear dispersion, the steeper the wave the faster it travels. He also showed that a wave with maximum height has a crest angle of 120◦ . The nonlinear effect influences the wave shape with sharp and higher crest and flatter at the trough. As a response to the observation and the experiment of soliton wave by John Scott Russel, Boussinesq [1872] derived equations that are now known as the Boussinesq equations. Boussinesq simplified the Euler equations for irrotational, incompressible fluid. He approximated the depth dependence of the Laplace equation in the interior fluid potential. In the approximation, a Taylor expansion up to a certain order around still water level is applied at the velocity potential function with incorporating the frequency dispersion. That leads to bi-directional and dispersive dynamic equation for the surface elevation and the velocity. These ’classical’ Boussinesq equations are valid for weakly nonlinear and fairly long waves. Of major importance is the fact that the whole dynamics is expressed solely by quantities at the surface, without any explicit equations for the interior flows. Nowadays, therefore, such models are more generally called Boussinesq (type of) equations. Korteweg and de Vries [1895] derived a simplified Boussinesq equation. The simplification was obtained in such a way that the bi-directional dynamic equations lead to one unidirectional dynamic equation. The KdV equation is valid for weakly nonlinear and weakly dispersive long waves and can be expressed as ηt + (c0 + c1 η)ηx + νηxxx = 0,

(1.10)

where c0 , c1 and ν are constants. The KdV equation has the same properties as the Boussinesq equation that both have (periodic) cnoidal and soliton profiles as solution. These theoretical results answered the observation and the experimental result of solitons by Scott Russel.

1.2

Variational water wave modelling

Many mathematical models of surface gravity wave have been developed recently. Most of the effort is to improve the accuracy of the model in terms of dispersion and nonlinear properties. A fascinating feature of the study of water waves is that the motion can exhibit qualitative differences at different scales such as deep water versus shallow water, long wavelength versus short wavelength. Therefore the existing wave models were constructed by various approximations to the limiting cases. In shallow water, there are equations of Boussinesq [1872], Korteweg and de Vries [1895], Benjamin et al. [1972], Serre [1953], Green and Naghdi [1976], Camassa and Holm [1993], and others. On finite depth and deep water, there are equations of [Stokes, 1847], nonlinear Schr¨odinger type of Dysthe [1979], Peregrine [1983] and others. Generally, these equations are valid for a limited range of the the relative water depth (kh, in which k the wave number, h the water depth). Most of the models were derived using some perturbation techniques that are valid for relatively small amplitude. However, in many applications it is desired to use a wave model that is uniformly valid for all depths and also accurate for large amplitudes. To that end, a different

1.2 Variational water wave modelling

7

approach of modelling, the so-called variational formulation is used in this work. In this section, the development of the variational formulation of water waves is summarized. Luke [1967] formulated a Lagrangian variational description of the motion of surface gravity waves on an incompressible and irrotational fluid with a free surface as Z Z Z η 1 2 ∂t Φ + |∇3 Φ| + gz dz dx. CritΦ,η P(Φ, η) dt where P(Φ, η) = 2 −h (1.11) The variables in this variational principles are the surface elevation η (depending on the two horizontal dimensions x and y) and the fluid potential Φ inside the fluid, so depending on horizontal and vertical dimensions. Note that this is a ’pressure principle’ since the integrand P denotes the pressure in the fluid, according to Bernoulli’s formulation of the Euler equation for irrotational fluid. The pressure principle has been remarked before by Bateman [1929] but without considering variations of the free surface η. The following is a derivation of the water wave problem from the Luke’s Lagrangian functional. The vanishing of the first variation of the functional with respect to variation δΦ in Φ leads to Z η Z Z dt dx ∂t (δΦ) + ∇3 Φ · ∇3 (δΦ) dz = 0. −h

It can be rewritten by applying Leibniz’s integral rule for the first term Z η Z η ∂t (δΦ) = ∂t (δΦ) dz − (δΦ)z=η ∂t η − (δΦ)z=−h ∂t h −h

−h

and the use Gauss’s theorem for partial integration Z η Z Z Z z=η dx ∇3 Φ · ∇3 (δΦ) dz = − dx [(∇3 · ∇3 Φ)δΦ dz] + dx [(∂N Φ)δΦ]z=−h . −h

Here a boundary term at the lateral boundaries has been neglected. Then the vanishing for all variations δΦ leads to Laplace equation in the interior fluid, the impermeable bottom and the kinematic free surface conditions. The equations are explicitly expressed as ∆3 Φ = 0 for ∇3 Φ · Nb = 0 at

∇3 Φ · Ns = ∂t η at

−h 0. The corresponding kinetic energy is then Z 0 Z 1 ρ2 2 2 (Cu) dx + (Cu) dx. 2g 2g 0 This corresponds to a change of phase speed with a factor ρ and the linear reflection relation is given by 1−ρ . (3.20) R= 1+ρ The calculated reflection from simulation results in the next section will confirm this relation although nonlinear waves show a small deviation from the relation for linear waves.

52

Localization for spatial-spectral implementations

Conversely, if a desired reflection coefficient R is given, the required value of ρ is found from inversion of the explicit relation: ρ=

3.3.2

1−R . 1+R

(3.21)

Frequency dependent reflecting wall

The idea of the previous subsection can now be generalized for frequency or wave length dependent reflection, by multiplying the phase velocity with a quantity ρ (k) resulting in the kinetic energy after the wall as Z 1 2 ˆ K (u, η) = |Cρ u| dx with Cˆρ = ρ (k) C. 2g 0 By prescribing the reflection coefficient depending on frequency ω, 0 ≤ R(ω) ≤ 1, the quantity ρ¯(ω) is given by ρ¯(ω) =

1 − R(ω) . 1 + R(ω)

(3.22)

Then the corresponding quantity ρ depending on the wavenumber k can be obtained by ρ(k) = ρ¯ Ω−1 (3.23) − (ω) with Ω− the dispersion relation at the left, Ω− (k) = kC− (k). In the next section we illustrate this for the case that the longest waves are completely reflected while other wave lengths are reflected only partially; this may serve as a simple model for the complete refection of infragravity waves and partial reflection of shorter waves when coastal waves bounce against a break water.

3.3.3

Run-up on coast

In the modelling of the run-up of waves on a coast, a spatial truncation is applied in the total energy. Then the Hamiltonian is taken to be Z 1 1 2 gη 2 + (Cu) χ dx. (3.24) H(η, u) = 2 g and leads to the nonlinear Hamilton equations 1 ∂t η = − ∂x (C ∗ (Cu.χ)) g 1 ∂t u = −∂x gηχ + Cu. (∂η C) u.χ . g

(3.25)

The simulation interval is changing due to the moving shoreline. The governing dynamic equations (Eq. 3.25) hold on the wet side or active domain of the changing

3.4 Simulation results

53

simulation interval. It turns out that a moving Heaviside function χ(H) can be used to define the wet and dry domain as defined by 0 if H − Hmin < 0 χ(H) = . (3.26) 1 if H − Hmin ≥ 0 Taking χ(H) with H(x, t) = η(x, t) + D(x), Hmin is the minimum total depth that can be simulated depending on the maximal wave number used in the sim2 ulation. The minimum total depth is taken to be Hmin = (ν/kcut ) /g where ν the peak frequency and kcut = max(k)/4. The kcut is motivated in the Fourier method to prevent aliasing as described in [Kurnia and van Groesen, 2014a, van Groesen and van der Kroon, 2012].

3.4

Simulation results

In this section we show the performance of the accurate dispersive models with spatial-spectral implementation in the following inhomogeneous problems: waves over an underwater slope, waves breaking over a bar, breaking waves running up the coast, wave reflection against walls and the dam-break problem. The simulations results of waves over an underwater slope, wave breaking over a bar and the dam-break problem are obtained by the second order model ABHS2 as presented in [Kurnia and van Groesen, 2014a]. The simulation results of breaking waves running up the coast and wave reflection against walls are obtained by the second order equation as presented in this paper. The third and fourth order models ABHS3,4 from [Kurnia and van Groesen, 2014a] give comparable, slightly better, results, at the cost of somewhat larger computation times. Area influxing is used as described in [Lie et al., 2014], and to avoid periodic looping damping zones are employed at both ends of the interval.

3.4.1

Irregular waves running up a slope 0.1 W3

W2

W1

W4 W5

W6

0

bathymetry [m]

−0.1

−0.2

−0.3

−0.4

−0.5

−160

−140

−120

−100

−80

−60

−40

−20

0

20

x [m]

Figure 3.1: Lay out of the experiment of MARINbench 103001 with the location of wave gauges indicated.

54

Localization for spatial-spectral implementations

0.1 0.08 0.06

η [m]

0.04 0.02 0 −0.02 −0.04 −0.06 −0.08 −120

−100

−80

−60 x [m]

−40

−20

0

Figure 3.2: Shown are the spatial wave profiles at (t ≈ 282.5 s) at which an extreme crest height is obtained (red, solid-line), the maximum temporal crest (black, dashed-dot) and the minimum temporal trough (cyan, dots) after 700 s; the bathymetry is shown in a scale of (1:10) (dashed-line, black).

0.08

W6

−0.08 W5

η [m]

0.06

W4

−0.06 W3

0.06 W2

−0.06 200

220

240

260

280

300 time [s]

320

340

360

380

400

Figure 3.3: Elevation time traces at positions W2, x=-94.6 m, W3, x=-69.9 m, W4, x=30 m, W5, x=-24 m, and W6, x=-15.7 m are shown for the measurement (blue, solid-line) and the simulation (red, dashed-line) of MARINbench 103001.

The test case is a wave that after generation travels above a deep area at depth 0.6 m, then runs-up on an uniform slope (1:20) and continues above a flat shallow part with depth 0.3 m. This is a simplified geometry in laboratory scale (spatial factor 50) for the run-up of waves from the deeper sea to the shallower coast. The wave is an irregular wave with spectrum of JONSWAP-type and random phases, with peak period (Tp ) 1.7 s and significant wave height (Hs ) 0.062 m. This wave corresponds to wind waves entering the coastal area with peak period 12 s and significant wave height 3.1 m. The experiment was performed in MARIN (Maritime Research Institute in Netherlands) and registered as MARINbench 103001. Fig. 3.1 shows the lay out of the experiment and location of measurements. For the simulation, the measurement data at W1 is used as influx signal. Simulation results for this case have been presented before in

3.4 Simulation results

55

[van Groesen and van der Kroon, 2012, Adytia and van Groesen, 2012] using BiAB and OVBM equations. Fig. 3.2 shows the spatial wave profile at which an extreme crest is obtained in the approximately 400 wave long wave train. An extreme or freak like wave is usually defined as a wave with wave height more than 2Hs . The freak-like wave is observed at t≈ 282.5 s and at a position close to measurement at W3. Fig. 3.3 shows the time traces of simulations and measurement. The wave shapes are well reproduced during propagation above the deep area (W2, W3), during run-up from the foot of the slope (W4) to the top (W5) and above the flat shallow part (W6). The correlation between simulation and measurement gives quantitative information about the accuracy of the simulation. Deviations from the maximal value 1 of the correlation measures especially the error in phase, a time shift of the simulation; for correlation −1 the simulation is in counter phase with the measurement. In the present simulation, the correlation has been calculated in the time interval (100;700) s at W2, W3, ..., W6 to be 0.95, 0.94, 0.66, 0.90, 0.81. The correlation at W4 gives the lowest value as was also obtained in [van Groesen and van der Kroon, 2012, Adytia and van Groesen, 2012].

3.4.2

Irregular wave breaking over a bar 0.1 0.05 S1

S2

S3 S4 S5 S6

S7

0

bathymetry [m]

−0.05 −0.1 −0.15 −0.2 −0.25 −0.3 −0.35 −0.4

0

5

10

15 x[m]

20

25

30

Figure 3.4: Lay out of the experiments of [Beji and Battjes, 1994], with the location of the wave gauges.

Beji and Battjes [1994, 1993] conducted a series of experiments concerning the propagation of regular and irregular waves over a submerged trapezoidal bar, corresponding to either non-breaking, spilling breaking or plunging breaking waves. In this section we show simulation of an irregular spilling breaking wave, with peak period 1.7 s and significant wave height 0.035 m. Simulations using ABHS2,3 equations for regular wave plunging breaking have been shown in [Kurnia and van Groesen, 2014a]. The bathymetry is presented in Fig. 3.4; the water depth varies from 0.4 m in the deeper region to 0.1 m over the top of the bar. In the experiment the wave height is measured at seven positions: S1, S2, · · · , S7. Position S2 is at the upslope area (a 1:20 slope), positions S3, S4 are at the top of the bar and positions S5, S6 are at the downslope area (a 1:10 slope) and position S7 at the flat bottom close to

56

Localization for spatial-spectral implementations

S7

0.03 S6 −0.03

η [m]

S5

0.04 S4 −0.04 S3

0.04 S2 −0.04 60

70

80

90

100

110

120

130

140

150

time [s]

Figure 3.5: Elevation time traces at positions S2, S3, · · · , S7 are shown for the measurement (blue, solid-line) and the simulation (red, dashed-line) of the irregular breaking wave propagating over a bar.

S7

4 S6 2 0

Amplitude Sp.

S5

5 S4

2 0

S3 6 3 0

S2 0

5

10

ω [rad/s]

15

20

Figure 3.6: Corresponding spectra of the time traces in Fig. 3.5.

the downslope area. The measured surface elevation at S1 at the foot of the slope is used as influx signal for our simulation. In Fig. 3.5 we show the elevation time traces at all measurement positions in the time interval (60; 150) s. The simulated surface elevation is in good agreement with the measurement. The wave transformation, the shoaling process (at S2), breaking at the top of the bar (at S3 and S4) and then the wave decomposition (at S5, S6, S7) are all well reproduced. The main discrepancy between measurement and simulation is observed at the downslope area (S5, S6 and S7). The corresponding spectra are shown in Fig. 3.6. In Fig. 3.7, we show at the top-left the spatial evolution of the maximum tem-

3.4 Simulation results

57

0.05 Hs [m]

MTA [m]

0.06 0.04 0.02

0.04 0.03

0 −0.02 10

11

12

13 x[m]

14

15

16

17

18

Sk

9 −4

x 10

9

10

11

12

13 x[m]

14

15

16

17

18

8

9

10

11

12

13 x[m]

14

15

16

17

18

8

9

10

11

12

13 x[m]

14

15

16

17

18

0 −2

5 1

0

−Asym

MWL [m]

8

2

−5

0 −1

9

10

11

12

13 x[m]

14

15

16

17

Figure 3.7: Spatial evolution of wave characteristics as computed (red, lines) and measured (blue, symbols) of irregular breaking waves propagating over a bar. At the top-left △: maximum temporal crest, ▽: minimum temporal trough, at the bottom-left, ◦: mean water level. At the right, Hs: significant wave height (top), Sk: skewness (middle), As: asymmetry (bottom).

poral crest and the minimum temporal trough (left), at the bottom-left the mean water level; at the right, the significant wave height (top), skewness (middle) and asymmetry (bottom). The skewness Sk measures the crest-trough shape, and the asymmetry As measures the left-right differences in a wave, defined as: Sk =

h(η − η¯)3 i h(η − η¯)2 i3/2

As =

hH(η − η¯)3 i h(η − η¯)2 i3/2

(3.27)

where η¯ is the wave-averaged surface elevation, hi is time averaging operator and H the Hilbert transform. The plots show that the simulation captures the main wave characteristics in a good way.

3.4.3

Harmonic breaking wave running up a coast 0.1 0.05 W2

W1

W3

...

...

W10

W21

0 S2 S3 S4 S5 S6 S7

S1

S8

bathymetry [m]

−0.05 −0.1 −0.15 −0.2 −0.25

1

−0.3

35

−0.35 −0.4 −20

−18

−16

−14

−12

−10 x [m]

−8

−6

−4

−2

0

Figure 3.8: Lay out of the experiments of [Ting and Kirby, 1994]. The location of the wave gauges for surface elevation are indicated by ⋄ (red). The interior horizontal velocity is measured at 8 positions, indicated by ◦ (green), every 0.01 m in the vertical direction.

In this section we show simulation results of a harmonic wave running up a coast. Except for the surface elevation also the interior horizontal velocity is compared to

58

Localization for spatial-spectral implementations

Figure 3.9: Simulation results of breaking waves during run-up; shown are the spatial surface elevation (top), the interior horizontal velocity (middle) and the interior vertical velocity (bottom) at t≈ 60 s. Breaking nodes are indicated by circles (blue).

data of laboratory experiments conducted by Ting and Kirby [1994]. Harmonic waves were generated above a flat bottom with depth 0.4 m and propagate over a 1:35 sloping coast. In this section we show only the spilling breaker case, for which the wave period is T = 2.0 s and the incident wave height H = 0.125 m. The bathymetry is presented in Fig. 3.8, indicating 21 positions of wave elevation measurements and 8 positions of interior horizontal velocity measurements, measured every 0.01 m in the vertical direction. Fig. 3.9 shows results of the simulation: the spatial surface elevation, the interior horizontal velocity and the vertical velocity at t ≈ 60 s. Breaking in the simulation starts at x ≈ −6.9 m which agrees with the measurement, and then continues till the shore. The initiation of breaking in the simulation was obtained by the kinematic criterion U/C >= 0.55 in which U is the crest speed and C is the phase speed at the crest. The corresponding interior horizontal velocity has maximum value in the crest when the breaking starts. Correspondingly, the interior vertical velocity has maximum value in the front of the wave. Fig. 3.10 at the left shows time traces of surface elevation of simulation and measurement at W1 (deep area) to W21 (close to the shore). The wave shape is well reproduced and in phase during shoaling and breaking which takes place at W10. At positions close to shore, the simulation overestimates the wave crest as shown also in the maximum temporal crest plot and skewness plot in Fig. 3.10. However the simulation captures the main wave characteristics in a quite good way. Fig. 3.11 shows the variations of the time-mean horizontal velocity at different depths at several locations indicated in Fig. ¯ √ 3.8. The time-mean horizontal velocity u is normalized by the wave celerity (C = gD). In agreement with the measurement, the calculated time-mean horizontal velocity is in the onshore direction near the surface and in the offshore direction below the trough level. The main discrepancy between the calculated and the measured value is at positions close to the shore.

3.4 Simulation results

W21

0.06 −0.06

W19

0.08 −0.08

W17

0.09 −0.09

W15

0.1 −0.1

W13

0.1 −0.1

W11

0.1 −0.1

W9

0.1 −0.1

W7

0.1

elevation [m]

W18 W16

0.05

0

W14 −0.05

W12 −14

−12

−10

−8 x[m]

−6

−4

−2

W10 0.2 Hs [m]

0.15

W8

0.1 0.05 0

W6

0.09 −0.09

W5

0.08 −0.08

W3

0.08 −0.08

0.15

W20

−14

−12

−10

−8 x[m]

−6

−4

−2

−14

−12

−10

−8 x[m]

−6

−4

−2

−14

−12

−10

−8 x[m]

−6

−4

−2

3 2 Sk

W4

1 0

W2 2

W1 38

40

42

44

46

48 50 time [s]

52

54

56

58

−Asym

η −η ¯ [m]

0.06 −0.06

59

1 0 −1

Figure 3.10: For the harmonic breaking wave running up a coast, at the left the elevation of simulation and experiment as in Fig. 3.5 and at the right same information as in Fig. 3.7.

3.4.4

Wave-wall interactions

In the first subsection we deal with a uniformly partially reflecting wall, i.e. all waves are reflected with the same fraction R. In the second subsection we show results for frequency dependent reflection at the wall. Fully or partially reflecting walls In this section we show simulation of harmonic waves colliding at a fully or partially reflecting wall. The simulation results are compared with analytic solutions. The relation between the reflection coefficient R and the constant ρ in Eq. 3.20 is confirmed by simulation results as shown in Fig. 3.12. The simulation results are for harmonic waves with period 2 s which corresponds to wavelength ≈ 6.3 m, initial wave height 0.1 m, propagating above a flat bottom with depth 5 m and colliding against a wall (at x = 150 m), simulated by the linear Hamilton equations and the second order Hamilton equations for different values of ρ. In Fig. 3.13 we show the spatial wave profile at t = 522.2 s and time trace at

Localization for spatial-spectral implementations

0

S1

0 −0.2 (z − η¯)/D

−0.2 (z − η¯)/D

S2

−0.4 −0.6

S3

0

−0.4

−0.6

−0.8 −0.8

−0.4

−0.4

−0.6

−0.6

−0.8

−0.8

−1

−1 −0.4 −0.2

0 √ u ¯/ gD

0.2

−0.4 −0.2

0.4

0

S5

−0.4 −0.2

0.4

S6

0

0 0.2 √ u¯/ gD

0.4

−0.4 −0.2

0 0.2 √ u¯/ gD

0.4

S8

S7 0

−0.1 −0.2

(z − η¯)/D

−0.4 −0.6

−0.3 −0.4 −0.5

−0.2 (z − η¯)/D

−0.2

−0.2 (z − η¯)/D

0 0.2 √ u¯/ gD

(z − η¯)/D

0

S4

−0.2

−0.2 (z − η¯)/D

0

(z − η¯)/D

60

−0.4

−0.4

−0.6

−0.6

−0.8

−0.8

−0.6 −0.7

−0.8

−0.8 −1

−1 −0.4 −0.2

0 0.2 √ u ¯/ gD

−0.4 −0.2

0.4

0 0.2 √ u ¯/ gD

0.4

−0.4 −0.2

0 0.2 √ u¯/ gD

−0.4 −0.2

0.4

0 0.2 √ u ¯/ gD

0.4

Figure 3.11: Shown are the time-mean horizontal velocity of calculation ◦ (red) and measurement ∗ (blue) below horizontal spatial points S1, S2 · · · , S8 illustrated in Fig. 3.8. 1 0.9 0.8 0.7

R

0.6 0.5 0.4 0.3 0.2 0.1 0

0

0.2

0.4

ρ

0.6

0.8

1

Figure 3.12: Relation between the reflection coefficient R and ρ. Simulation results by the linear Hamilton equations ◦ (red), the nonlinear Hamilton equations ∗ (blue) are compared to the exact relation Eq. 3.20 (solid-line, black).

the wall position x = 150 m of the linear simulation of the harmonic waves with period 2 s. It shown that the reflected wave height is as desired 2 times the initial wave height for full reflection and 1.5 times for 50% reflection. In Fig. 3.14 we show the nonlinear simulations with the same initial wave characteristics. The nonlinear effects lead to a small modulation in the wave elevation. Fig. 3.15 shows linear simulations with different wave periods 4 s and 6 s. The harmonic waves with period 4 s corresponds to wavelength ≈ 22.2 m and period 6 s corresponds to wavelength ≈ 38.1 m. These are long wave compared with the depth of 5 m. The reflected wave height is approximately 2 times the initial wave height for full reflection; the wave with period 6 s shows a slightly higher amplitude at the

3.4 Simulation results

61

0.15

0.15

0.05

η [m]

0.1

0.05

η [m]

0.1

0

0

−0.05

−0.05

−0.1

−0.1 0

20

40

60

80 x [m]

100

120

140

160

0

0.15

0.1 0.05

η [m]

0.1 0.05

η [m]

20

40

60

80 x [m]

520

525 time [s]

100

120

140

160

0.15

0

0

−0.05

−0.05

−0.1

−0.1

500

505

510

515

520

525 time [s]

530

535

540

545

550

500

505

510

515

530

535

540

545

550

Figure 3.13: Reflected harmonic wave profiles at t = 522.2 s (at the top) and time trace at the wall position (at the bottom) for waves with period 2 s with λ/D = 1.3. At the left and at the right are simulation results for 100% and 50% reflecting wall, respectively. Simulations using the linear Hamilton equations are indicate by dashed-line (red), the linear analytic solution by solid-lines (blue), the maximum temporal crest by dashed-dot (black), the minimum temporal trough by dots (cyan) and the wall at x = 150 m by vertical line (yellow) 0.15

0.15

0.05

η [m]

0.1

0.05

η [m]

0.1

0 −0.05

0 −0.05 −0.1

−0.1 0

20

40

60

80 x [m]

100

120

140

0

160

0.1 0.05

η [m]

0.1 0.05

η [m]

20

40

60

80 x [m]

520

525 time [s]

100

120

140

160

0.15

0.15

0

0

−0.05

−0.05

−0.1

−0.1

500

505

510

515

520

525 time [s]

530

535

540

545

500

550

505

510

515

530

535

540

545

550

Figure 3.14: Same as in 3.13. Now for simulations (dashed-line, red) using the the second order Hamilton equations compared to the linear analytic wave (solid-line, blue) 0.15

0.1

0.1

0.05

0.05

η [m]

η [m]

0.15

0 −0.05 −0.1

−0.1 −20

0

20

40

60

80 x [m]

100

120

140

160

180

−50

50

100

150

200

0.15 0.1

0.05

0.05

η [m]

0.1

0 −0.05

0 −0.05

−0.1 500

0

x [m]

0.15

η [m]

0 −0.05

−0.1 505

510

515

520

525 time [s]

530

535

540

545

550

500

505

510

515

520

525 time [s]

530

535

540

545

550

Figure 3.15: Same as in 3.13. Now for simulations with period 4 s (left) and 6 s (right) corresponding to λ/D = 4.4 and 7.6 respectively.

62

Localization for spatial-spectral implementations

wall while small shifts in phase are also observed. Frequency dependent reflecting wall

50

1

1

0

0

0.5

1

ω [rad/s]

1.5

0.5

R and ρ

Amplitude Sp.

0.5

R and ρ

Amplitude Sp.

40

20

0

2

0

0.5

1

ω [rad/s]

1.5

2

0

Figure 3.16: Shown are the spectrum of the influx signal (solid-line, blue), the prescribed reflection coefficient R(ω) (solid-line, green) and the calculated ρ¯(ω) (dashed-dot, green). At the left, ρ¯1 for R1 = 1 − min ω 2 , 0.5 , and at the right, ρ¯2 for R2 = 1 − min ω 2 , 1 .

η [m]

0.1 0 −0.1 0

500

1000

1500

2000

2500

x [m]

η [m]

0.1

0

−0.1 300

400

500

600

700 time [s]

800

900

1000

1100

1200

66.92 0.5

33.46 0

0

0.2

0.4

0.6

0.8 1 ω [rad/s]

1.2

1.4

1.6

Reflection Coef.

Amplitude Sp.

200

0

Figure 3.17: Shown are simulation results with the reflection coefficient R1 (blue, solidline), R2 (green, dashed-line) and without wall (red, dashed-dot). At the top, the wave profiles at time t = 1000 s and maximum temporal amplitudes for: simulation with the wall (black, solid-line for R1 and cyan, dashed-line for R1 ), without wall (magenta, dashed-dot) and the wall at x = 2500 m (yellow, vertical line). The middle plot shows time traces at the wall position. The bottom plot shows the spectrum at the wall position with at the left axis the amplitude spectra, and at the right axis the value of the reflection.

In this section we show simulation results of waves colliding at a frequency dependent reflecting wall. The waves are irregular waves with JONSWAP spectrum with gamma 3.3, significant wave height 0.1 m, peak period 12 s above a flat bottom with depth 25 m. We show comparison of the second order nonlinear simulationwith and without wall, for walls with two reflection properties R1 = 1 − min ω 2 , 0.5 and R2 = 1 − min ω 2 , 1 as shown in Fig. 3.16.

3.4 Simulation results

63

Fig. 3.17 shows that with R1 the simulation shows the correct full reflection of long waves and partial reflection R ∈ [0.5, 1) for shorter waves. With R2 the simulation shows partial reflection with R ∈ (0, 1] for ω < 1, and full transmission of shorter waves.

3.4.5

Dam-break problem

0.15 1

0

t1

t2

t3

t4

t5

t6

η/h

η/h0

0.1 t7

0.05

0.5 t*=10

0 0

20

40 x/h0

0.4

60

0 0

80

t*=24

t*=48 t*=62

50

100

t*=95 150

x/h

0

0

η/h

η/h0

1 0.2 t1 0 0

t2 20

t3

t4 40 x/h

t5

t6

0.5

t7

60

t*=10 0 0

80

t*=24 t*=32

t*=95 150

1

0.6

0

0.4

η/h

η/h0

100 x/h0

0

0.5 t*=10

0.2 t1 0 0

t*=62

50

t2 20

t3

t4

40 x/h

0

t5 60

t6

t7 80

0 0

t*=24 50

t*=40

t*=62 100

t*=95 150

x/h

0

Figure 3.18: At the left are shown spatial surface elevations for undular bore simulations with initial height (η/h0 ) 0.1 (top), 0.2 (middle), 0.3 (bottom) at various times: t1 = 10, t2 = 20, t3 = 30, · · · , t7 = 70. At the right are shown the elevations for breaking bore simulations with initial height 0.43 (top), 0.52 (middle), 0.6 (bottom); the breaking nodes are indicated by ◦ (blue).

In this section we simulate undular bores propagating into constant-depth, still water. This case is also known as the dam break problem that has been widely studied as a standard illustration of competing effects of dispersion and nonlinearity. In this testcase we reproduced and extended simulations of previous work by Wei et al. [1995]. The initial conditions describe a gentle transition between a uniform flow and still water 1 1 η = u + u2 . (3.28) u = u0 [1 − tanh(x/a)] , 2 4 Here η is the surface elevation and u is the velocity. In our models the velocity is the tangential velocity, which is different from the horizontal velocity in [Wei et al., 1995]. u0 is the velocity of the uniform flow from the left boundary and a is a number sufficiently large so that the initial motion can be described by Airy’s theory. The same value a = 5 is used and u0 is chosen so that the surface elevation at the left boundary is as required η0 = 0.1, 0.2, 0.3. The simulations as shown in Fig. 3.18 at the p left are presented in the same scale as in Fig. 7 of [Wei et al., 1995], t∗ = t/ h0 /g, x∗ = x/h0 with h0 = 1. Qualitatively the simulations using the Hamilton equations are similar with the simulations using the fully nonlinear potential flow presented in Fig. 7 [Wei et al., 1995].

64

Localization for spatial-spectral implementations

To simulate more extreme cases, we increased the initial surface elevation to values η0 = 0.43; 0.52; 0.6 that lead to breaking bores, shown in Fig. 3.18 at the right. The bores start to break at time t∗ = 24, 32 and 40 at different positions for the simulations with three different initial conditions respectively. The waves are shown to break at the front.

3.5

Conclusion

It is quite remarkable that the method proposed here, the rather straightforward generalization given in Eq. 3.12 of the explicit expression of the phase velocity from Airy’s linear theory, leads to a model and implementation that performs so well for even the most difficult cases as shown in Section 3.4. A major reason must be that the model has the exact asymptotic behaviour of the limit of linear waves above flat bottom, as well as the shallow water limit, both limits valid for all types of waves i.e. for all wave lengths; this despite the strict conclusion about the second order accuracy from the classical ’order’ reasoning as presented in Section 3.2.3 which may be too pessimistic for the model that is inherently based on a non-algebraic formulation. Provided the Fourier Integral Operators are correctly dealt with, in particular the symmetry properties, the Hamilton equations are obtained in a very explicit way. Consequently, the actual numerical implementation is very simple: using FFT’s for the spatial discretization and an explicit time solver, the explicit formulas are literally copied without any adjustments or ’trics’. For computational effectiveness, the interpolation of the symbols in the FIO’s is essential; in all cases considered so far (including those in this paper), just 2 or 3 interpolants are enough to get accurate results. As a consequence, most simulations can be done in (essentially) less than 25% of the physical time in environmental geometries. With the methods described in this paper in Section 3.3 we have overcome the localization problems that are typical for global methods such as Fourier methods. At this moment similar methods are used to model and simulate wave-ship interactions, results of which will be published elsewhere. Although the simulations are performed in a dimension reduced way, the calculation of the internal flow as described in Section 3.2.5 will be useful for various applications. Simulations as shown in this paper can be performed with HAWASSI-AB software.

Chapter

4

Design of wave breaking experiments and a-posteriori simulations 1 Summary In this chapter, we present results of 30 wave breaking experiments that were designed by HAWASSI-AB software. The experiments were carried out in a wave tank of Technical University of Delft (TUD). The use of the efficient simulation code can optimize the experiments by designing the influx such that waves will break at a predefined position. The consecutive actual measurements agree well with the numerical design of the experiments. Using the measured elevation close by the wave maker as input, the software recovers the experimental data in great detail, even for rather short (up to L/D=1) and very steep breaking waves with steepness parameter (ak) till 0.4.

4.1

Introduction

For the design of fixed or flexible structures in the coastal area such as wind mills and oil platforms, knowledge of expected forces in extreme waves are of paramount importance. Experiments in wave tanks are often used to obtain impact data in well-controlled circumstances. Since the interest is mainly in extreme wave conditions, it is required to prepare the incoming wave such that the desired extreme behaviour takes place at the defined position of the structure. Limitations on the wave generator and the complicated distortions during the wave propagation towards the structure makes this a challenging task. 1 The contents of the chapter is partly presented as a proceeding article [Kurnia et al., 2015] and an internal report [Kurnia and van Groesen, 2015a]

66

Design of wave breaking experiments and a-posteriori simulations

This chapter presents results of 30 wave breaking experiments conducted in the long wave tank of TU Delft, Department of Maritime and Transport Technology (6,7 and 10-12 March 2014). Simulations performed before the experiment to determine the required wave maker motion and a-posteriori simulations that use a measured time trace as influx for calculation further downstream are also presented. The 30 different experiments cover a broad range of breaking waves of various types. Those are roughly grouped together as follows: 11 focussing waves, 7 bichromatic wave trains, 9 irregular waves, 2 cases of ’soliton on finite background’, 1 harmonic wave with added focussing wave. Characteristic for all cases is the rather broad spectrum (although restricted by wave maker properties). In each group, the cases differ in amplitude, period and steepness. The range of wavelength for these cases runs from 1 to 4 times the depth and the steepness parameter (ak) till 0.4. 27 experiments showed breaking as designed; the harmonic focussing case, and the two test cases TUD1403Ir7 and TUD1403Foc12 were (designed to be) non-breaking. The aim of this Chapter is to show that HAWASSI-AB, a Hamiltonian Boussinesq model with breaking mechanism, is sufficiently accurate to support the design task prior to the actual experiment. Moreover, the a-posteriori use of the measured elevation close to the wave maker to initiate the simulation, leads to reconstruction of the waves that is accurate at all measurement positions. The organization of this chapter is as follows. Section 4.2 describes the laboratory experimental set-up. Section 4.3 gives a brief description of the simulation model. In Section 4.4, comparison of measurement results with the a-priori and a-posteriori simulation will be presented. Conclusions will finish this chapter.

4.2

Experimental set up

The wave tank at Technical University of Delft was used to perform the experiments. The tank is 142 m long, 4.22 m wide and the depth during the experiment was 2.13 m. At the end of the tank, waves are absorbed by an artificial beach. Waves are generated by a flap type wavemaker. Fig. 4.1 shows a cross-section of the wave tank. Resistance type of wave probes were used to measure surface elevation at various positions at the centre-line of the tank. The wave probes operate by measuring the current that flows between two stainless steel wires that are immersed in the water. This current is converted to an output voltage that is directly proportional to the immersed depth. Calibration of a potentiometer on the wavemaker and the wave probes in the fluid has been done before the start of the experiments. This calibration has been used to determine the transfer function for optimized performance. The same measurement positions were used for a total of 30 different experiments. The experiments were designed in such a way that most breaking waves could be caught at the same position, which then were selected as the measurement positions. The position of breaking of the waves did not always coincide precisely with the wave probe positions. Nevertheless, from the recorded video and markers in

4.3 Simulation model

67

Figure 4.1: The wave tank of TUD. View from a carriage at approximately 70 m to wave maker.

the wavetank, the breaking position and breaking moment could be approximated afterwards. Comparison of observed and simulated breaking events will be shown in the next section on design and reconstruction. A schematic lay-out is shown in Figure 4.2. The elevation is measured at positions W1 at x = 10.31 m, W2 at x = 40.57 m, W3 at x = 60.83 m, W4 at x = 65.57 m, W5 at x = 70.31 m and W6 at x = 100.57 m.

Figure 4.2: Layout of the experimental set-up.

In Appendix A.1 an overview of the experiments is given with all main wave parameters.

4.3

Simulation model

The model used for the numerical simulations is part of HAWASSI-AB, the Hamiltonian Wave Ship-Structure Interaction, using Analytic Boussinesq model. For the present cases only the wave facility has been used. A full description of the code and the breaking model can be found in [Kurnia and van Groesen, 2014a]. The most characteristic properties of the model are now summarized. The model is of Boussinesq type, which means that the interior fluid motion is not calculated but modelled so that a spatial reduction is obtained. The model has a Hamiltonian structure, with main consequence that it is exactly energy conserving for non-breaking waves.

68

Design of wave breaking experiments and a-posteriori simulations

The main disadvantage of most Boussinesq equations is overcome by using a spatial-spectral implementation so that dispersion is exact for all wave lengths in the order of nonlinearity of the equation. For the experiments in this chapter, the third-order equation (ABHS3 in [Kurnia and van Groesen, 2014a]) has been used. Wave generation is done in an embedded way by influxing the given elevation signal at the influx position through a source in the continuity equation; in [Lie, 2013] this generation is described in detail. Here area influxing has been used with an adaptation area to prevent the generation of spurious waves for the extreme influx heights used in some of the experiments. For breaking the mechanism as proposed by Kurnia and van Groesen [2014a] is used; the initiation of breaking is determined by a kinematic breaking criterion. Instead of the absorbing beach of the wave tank, the simulated wave is smoothly damped to avoid any reflections from the end. Simulations with the HAWASSI-AB code are reasonably fast; depending on the specific case, computation times are 0.5 to less than 3 times the physical time. The simulations are also robust for change of parameters such as grid size, initiation of breaking, etc. as shown in [Kurnia and van Groesen, 2014a].

4.4

Design and reconstruction

Of the 30 experiments listed in Appendix A.1 we select a few characteristic cases for presentation here. A full account of all simulations is available in Appendix A.2 and A.3. In the first subsection we compare measurement results with the a-priori simulated wave; we call this the design case. It will be seen that there are some discrepancies between the designed waves and the experiments, but the differences are for most practical applications acceptable. In the second subsection we compare the measurements with the simulated waves that use the measured elevation at W1 as input for simulation; we call this the reconstruction. These simulation results compare better with the experiments. This indicates that the transfer function used to translate information from the designed waves to the wave maker motion must account for the differences. In all cases, the waves were approximated with an analytic model choosing the steepness parameters such that breaking could be expected. Then the simulation using HAWASSI-AB gave a complete overview of the designed waves including the positions of breaking. In the following plots of wave elevations, measurements are indicated by blue (solid) lines, and simulations by red (dashed) lines.

4.4.1

Design cases

To determine input for the wavemaker, the elevations signal at 10 m of the a-priori simulated wave has been taken. Using the transfer function of the the wavemaker, the actual wavemaker motion has been calculated. The range of frequencies for the

4.4 Design and reconstruction

69

input of the wave maker is (2.4, 6) [rad/s] which restricts the generation of waves to periods in between 1 s and 2.6 s. We now describe the results for two cases. Experiment TUD1403Foc7 is a focussing wave often used in laboratories to generate very high waves as an effect of dispersive wave focussing, in this case with an amplification of about 2.73. As shown in Figure 4.3, qualitatively the agreement between design and experiment is good, but differences in the spectra further downstream are quite noticeable at higher frequencies. The breaking position in the design is 65 m and the observed breaking in the experiment takes place at 59 m. The wave was designed to break at the focussing position but in the experiment the wave breaks one peak wavelength before the focussing. 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1

W1

W6 1 0.5

W5

W4 S ||S inf lux ||∞

η[m]

0

1 0.5 0 W2 1 0.5

40

W3

50

60

70

80

90 t[s]

100 110 120 130

0 0

W1 1

2

3

4 5 ω [rad/s]

6

7

8

Figure 4.3: Elevation time traces (left) and normalized spectra (right) of TUD1403Foc7 at positions W1, · · · , W6 are shown for the measurement (blue, solid) and for the simulation (red, dashed dot).

Experiment TUD1403Bi3 is a bichromatic wave; for specific parameters see Appendix A.1. Severe breaking takes place at multiple positions. Figure 4.4 shows plots of wave elevations and spectra. The spectrum shows substantial energy loss due to breaking; spectra and time traces at different positions show a gradual down-shift of the bi-chromatic pattern, with higher order waves developing and disappearing further downstream. The spectrum of design and experiment agree quite well; the time traces at larger distances differ in the small wave separation regions between the wave groups. Figure 4.5 shows the positions and times of breaking in the simulation (solid dots, red). Breaking in the experiment as observed in reality and in a movie is indicated also (open dots, blue) but the observation of breaking events in the experiment is limited from x ≈ 50 m to x ≈ 70 m.

70

Design of wave breaking experiments and a-posteriori simulations

0.1 W6 0 −0.1

W6 1

0.1 W5 0 −0.1

0.5 0

W4 S ||S inf lux ||∞

η[m]

0.1 W4 0 −0.1 0.1 W3 0 −0.1 0.1 W2 0 −0.1

1 0.5

W3

0 W2 1

0.1 W1 0 −0.1 40

W5

0.5

60

80

100 120 t[s]

140

160

180

0 0

W1 1

2

3

4 5 ω [rad/s]

6

7

8

Figure 4.4: Same as Fig. 4.3. Now for TUD1403Bi3. 120 110

Breaking position [m]

100 90 80 70 60 50 40 30 20 40

60

80

100 time [s]

120

140

160

Figure 4.5: Wave breaking positions of TUD1403Bi3 for the simulation (red, solid dots) and the observation in reality and in a movie (blue, open dots).

4.4.2

Reconstruction cases

We now reconstruct the experiments by taking the measured elevation at W1 as input signal for the numerical code. Experiment TUD1403Foc7 This focussing wave with ka ≈ 0.11 shows single wave breaking. The elevation time traces and the spectra are well reconstructed as shown in Figure 4.6. The differences in the spectra further downstream are rather small. The wave breaks at x = 59.2 m in the simulation and at x ≈ 59.5 in the experiment. Experiment TUD1403Ir10 This irregular wave with ka ≈ 0.27 shows successive wave breaking for a few waves. During propagation the spectrum becomes slowly broader, with limited energy decay. The spectra and time traces comparisons are shown in Figure 4.7 and the breaking positions in Figure 4.8.

4.5 Conclusions

71

Experiment TUD1403Bi3 This bichromatic wave shows abundant continued wave breaking of the steep waves with ka ≈ 0.3. The elevation time traces and the spectra are well reconstructed as shown in Figure 4.9. Observe the substantial down-shift in the spectrum which may be caused by the breaking, and the substantial energy dissipation. The breaking position of simulation and the limited observation are shown in Figure 4.10.

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

1 0.5

W6

W5

S ||S inf lux ||∞

η[m]

0

1 0.5

W4

0

60

W3

1 0.5

70

80

90

100 t[s]

110

120

130

140

0 0

W2

1

2

3

4 5 ω [rad/s]

6

7

8

Figure 4.6: Same as Fig. 4.3. Now for reconstruction.

4.5

Conclusions

The use of an accurate numerical code can optimize the experiments. A comparison of the design simulations prior to the experiment and the measurements show that the time traces at the measurement positions are quite accurate; the substantial changes in the measured spectra at the successive positions compare reasonably well with the changes of the prior design simulations. However, there are some discrepancies between the designed waves and the corresponding experiments. In the focussing wave case (TUD1403Foc7), the actual breaking position takes place one peak wavelength in front of the designed position, but the focussing position is the same as designed a priori. Taking the actual experimental wave elevation time trace at the first measurement point as input for the simulations for reconstruction a posteriori the experiment, both breaking and focussing positions of simulation and measurement are in good agreement. This indicates that the transfer function used to translate information from the designed waves to the wave maker accounts for the differences that were observed in the design cases.

Design of wave breaking experiments and a-posteriori simulations

0.2 0 −0.2 0.2

η[m]

0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0

1

W6

0.5

W6

0

W5

W5

S ||S inf lux ||∞

72

W4

1 0.5

W4

0

W3

W3

1

W2

0.5

−0.2 40

60

80

100

120

140

160

180

200

W2

0 0

220

1

2

3

t[s]

4 5 ω [rad/s]

6

7

8

Figure 4.7: Same as Fig. 4.3. Now for TUD1403Ir10 (reconstruction). 120 110

Breaking position [m]

100 90 80 70 60 50 40 30 20 100

150

200

250

time [s]

Figure 4.8: Same as Fig. 4.5. Now for TUD1403Ir10 (reconstruction).

The irregular wave case (TUD1403Ir10) showed successive wave breaking for a few waves leading to broadening of the spectrum during propagation with limited energy decay. The simulations showed quantitatively good correlations with measurements. The bichromatic wave case (TUD1403Bi3), showed abundant continued wave breaking of the steep waves leading to the substantial down-shift in the spectrum and the substantial energy decay. In Table 4.1, we show the correlations at all measurement positions and the relative computation time (Crel). The correlation between the time traces of the measurement and the simulation is defined as the inner product between the normalized signals. Deviations from the maximal value 1 of the correlation measures especially the error in phase, a time shift of the simulation; for correlation -1 the simulation is in counter phase with the measurement. The relative computation time is defined as the cpu-time divided by the total time of the simulation; the calculations

4.5 Conclusions

73

1

0.1 W6 0 −0.1

0.5

W6

0 W5

S ||S inf lux ||∞

η[m]

0.1 W5 0 −0.1 0.1 W4 0 −0.1

1 0.5

W4

0

0.1 W3 0 −0.1

W3

1

0.1 W2 0 −0.1 60

0.5

80

100

120

140

160

W2

0 0

180

1

2

3

t[s]

4 5 ω [rad/s]

6

7

8

Figure 4.9: Same as Fig. 4.3. Now for TUD1403Bi3 (reconstruction). 120 110

Breaking position [m]

100 90 80 70 60 50 40 30 20

60

80

100

120 time [s]

140

160

180

Figure 4.10: Same as Fig. 4.5. Now for reconstruction.

were performed on a desktop computer with CPU i7, 3.4 GHz processor with 16 GB memory. The simulations show quantitatively good correlations in phase with measurements; and the calculation times rather short.

74

Design of wave breaking experiments and a-posteriori simulations

Table 4.1: Correlations at measurement positions for the various test cases between simulations and measurements. D stands for the design cases (experiment after simulation) and R for the reconstruction. Crel is the relative computation time.

W1 W2 W3 W4 W5 W6 Crel

TUD1403Foc7 D R 0.93 0.91 0.99 0.88 0.97 0.87 0.98 0.89 0.98 0.92 0.97 1.14 1.13

TUD1403Ir10 D R 0.94 0.92 0.97 0.85 0.96 0.84 0.95 0.86 0.94 0.81 0.86 2.48 2.43

TUD1403Bi3 D R 0.97 0.86 0.96 0.74 0.90 0.68 0.87 0.67 0.84 0.63 0.78 1.83 3.2

Chapter

5

Conclusions and recommendations 5.1

Conclusions

In this dissertation various aspects of water wave modelling are considered. The main topic is the development of an accurate and efficient model that can simulate wave propagation in any range of wave lengths and in any water depth. Moreover, it is desired that the model can deal with various inhomogeneous problems such as bathymetry and walls, leading to wave structure interactions. A challenge in the study of water waves is that the motion can exhibit qualitative differences at different scales such as deep water versus shallow water, long wavelength versus short wavelength, etc.. That leads to a restriction in the applicability of the existing wave models. It is remarkable that the accurate dispersive wave models, the AB (Analytic Boussinesq) models as presented in this dissertation, showed outstanding performance in terms of efficiency and accuracy. The AB models are uniformly valid for any depth, for large amplitudes and have wide applicability. A major reason is that the AB models were derived consistently from the Hamiltonian formulation. The approximated Hamilton equations were expressed in the exact phase speed operators with correct order of non-linearity in wave elevation. Thanks to the spatial-spectral implementation the exact dispersion property can be retained without any approximation. The dispersion is essential to obtain highquality wave propagation results. This improves the properties of more classical Boussinesq type of equations. The Hamiltonian consistent approximation guarantees correct evolution of momentum and (approximated) energy. Furthermore, the AB models can deal with various difficult cases such as breaking or non breaking waves that propagate over a submerged bar or a slope, run-up on the coast, with presence of partially or fully reflective walls, including the dam-break problem. To deal with breaking waves, an extended eddy viscosity breaking model that is applicable for fully dispersive waves was implemented. A kinematic breaking

76

Conclusions and recommendations

criterion that the wave will break when the horizontal particle speed exceeds (a fraction of) the crest speed was used as a trigger mechanism. To deal with localized effects i.e walls, coasts, submerged bar, etc., a localization method was applied in the global Fourier integral operators that are associated with the nonlinear phase speed operator. It is known that Fourier expansion techniques, different from finite difference or finite element method, lead to some problem when complicated geometric structures need to be included. The inclusion of such fixed structures in a spatial-spectral setting has been shown in this dissertation, it serves perhaps as a first contribution in this topic. In many applications such as the calculation of wave force on structures requires information of interior properties. A method to calculate or recover the internal flow in the time dynamic or post-processing step of the Boussinesq model has also been shown in this dissertation. An extensive comparison with (at least 50) laboratory data has been performed. The previous Chapter presented the 30 measurement data of wave breaking experiments in TUD wave tank that were designed using the AB models. It was shown that an efficient and accurate code can optimize wave-tank experiments. Simulations as shown in this dissertation can be performed with HAWASSI-AB software. The demo version can be downloaded on http://hawassi.labmath-indonesia.org.

5.2

Recommendations

For further research the following outlook is given: • In Chapter 3 a generalized AB model was derived. It has been indicated that the model has second order accuracy from the classical order reasoning. This can be improved by starting the derivation from the anzatz of nonlinear extension of the Airy potential and then substituted into the kinetic energy. • In Chapter 2 the kinematic criterion requires that the wave will break when the horizontal particle speed exceeds (a fraction of) the crest speed. A universal value of this parameter is not known yet. Further investigations on the breaking criterion are much desired. • The present models aim to simulate long crested waves. The simulation of short crested waves is expected to be a straightforward extension to two horizontal dimensions. • The method to model wave interactions with fixed structures has been presented. An extension to deal with floating structures such as ships can be done in the future. A Hamiltonian formulation of wave-ship interaction has been derived recently by van Groesen and Andonowati [2015].

Appendix

A

Supplementary files of the experiments This Appendix provides information of the wave breaking experiments that were presented in Chapter 4. The characteristic quantities of all main wave parameters are presented in Section A.1. The comparison between the experiments and apriori simulations is presented in Section A.2. The full comparison between the experiments and a-posteriori simulations is presented in Section A.3.

A.1

The characteristic quantities of the designed waves

The following table summarises the characteristic quantities of all the designed waves. The successive columns provide the following information: t max: maximum time, Tp: peak period, (T 0, dt): T 1 = T 0 + dt/2, T 2 = T 0 − dt/2 (Bichromatic periods), λp: peak wavelength, kp.a: steepness, H0: maximum wave height of influx signal, MTT: maximum temporal trough, MTC: maximum temporal crest, H1: maximum wave height of maximal signal, H1/H0: amplification, xb: successive breaking positions (separated by semicolon), or the range of breaking position as indication of many breaking events (denoted by x1-x2), and tb: the corresponding breaking time. The information is based on a-priori simulations.

78

Supplementary files of the experiments

A.2 Comparison of experiments and a-priori simulations

A.2

79

Comparison of experiments and a-priori simulations

η[m]

Bichromatic wave: TUD1403Bi3 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1

W1

40

60

80

100 t[s]

120

140

160

180

120

W6 110

1

100

0.5

Breaking position [m]

W5

0

S ||S influx ||∞

W4 1 W3

0.5 0

W2

90 80 70 60 50 40

1 W1

0.5 0 0

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 40

60

80

100 time [s]

120

140

Figure A.1: Elevation time traces (top) and normalized amplitude spectra (left below) at positions W1, W2, W3, W4, W5, and W6 are shown for the measurement (blue, solid) and for the design simulation with model ABHS3 (red, dashed dot). At the right below, the positions of breaking of the design simulation (red, solid dots) and the limited observation (x ∈ (50, 70)) in reality (in the movie, blue, open dots).

Table A.1: Wave properties: period, peak wavelength, steepness. Correlation at W1-W6 and relative computation time (Crel).

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.3

W1 0.97

W2 0.86

W3 0.75

W4 0.68

W5 0.67

W6 0.63

Crel 1.83

160

80

Supplementary files of the experiments

η[m]

Irregular wave: TUD1403Ir10

0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 40

W6

W5

W4

W3

W2

W1 60

80

100

120

140

160

180

200

t[s] 120

W6 110

1

100

W5 Breaking position [m]

0.5 0

S ||S influx ||∞

W4 1 0.5

W3

0 W2

90 80 70 60 50 40

1 0.5 0 0

W1

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 40

60

80

100

120 140 time [s]

160

Figure A.2: Same as Fig. A.1. Now for TUD1403Ir10.

Table A.2: Same as Table A.1. Now for TUD1403Ir10.

Tp 1.96

λp 5.87

kp .a 0.24

W1 0.94

W2 0.92

W3 0.85

W4 0.84

W5 0.86

W6 0.81

Crel 1.87

180

200

220

A.2 Comparison of experiments and a-priori simulations

81

η[m]

Focussing wave: TUD1403Foc7 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1

W1

40

50

60

70

80

90

100

110

120

130

t[s] 120

W6 110

1

100

W5 Breaking position [m]

0.5 0

S ||S influx ||∞

W4 1 0.5

W3

0 W2

90 80 70 60 50 40

1 0.5 0 0

W1

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 40

60

80

100

120 140 time [s]

160

Figure A.3: Same as Fig. A.1. Now for TUD1403Foc7 case.

Table A.3: Same as Table A.1. Now for TUD1403Foc7 case.

Tp 1.96

λp 5.89

kp .a 0.11

W1 0.93

W2 0.91

W3 0.88

W4 0.87

W5 0.88

W6 0.92

Crel 1.5

180

200

220

82

Supplementary files of the experiments

A.3

Comparison of experiments and a-posteriori simulations

η[m]

Focussing wave group: TUD1403Foc1

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

2

4

ω [rad/s]

6

8

10

20 20

40

60

80

100

120 140 time [s]

160

180

200

Figure A.4: Elevation time traces (top) and normalized amplitude spectra (left below) at positions W2, W3, W4, W5, and W6 are shown for the measurement (blue, solid) and for the a-posteriori simulation with model ABHS3 (red, dashed dot). At the right below, the positions of breaking of the design simulation (red, solid dots) and the limited observation (x ∈ (50, 70)) in reality (in the movie, blue, open dots).

Table A.4: Wave properties: peak period, peak wavelength, steepness. Correlation at W2-W6 and relative computation time (Crel).

Tp 1.85

λp 5.3

kp .a 0.19

W2 0.98

W3 0.97

W4 0.96

W5 0.96

W6 0.97

Crel 1.35

220

A.3 Comparison of experiments and a-posteriori simulations

83

η[m]

Focussing wave group: TUD1403Foc2

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

50

60

70

80 t[s]

90

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

110

120

1 0.5

100

W2

30

2

4

ω [rad/s]

6

8

10

20 20

40

60

80

100

120 140 time [s]

Figure A.5: Same as Fig. A.4, now for TUD1403Foc2 case.

Table A.5: Same as Table A.4. Now for TUD1403Foc2 case.

Tp 1.7

λp 4.46

kp .a 0.16

W2 0.98

W3 0.94

W4 0.94

W5 0.94

W6 0.88

Crel 0.68

160

180

200

220

84

Supplementary files of the experiments

Focussing wave group: TUD1403Foc5

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

50

60

70

80

90

100

110

120

t[s] 120

1 0.5

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

80 70 60 50 40

1 0.5

90

W2

1

30

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.6: Same as Fig. A.4, now for TUD1403Foc5 case.

Table A.6: Same as Table A.4. Now for TUD1403Foc5 case.

Tp 1.92

λp 5.7

kp .a 0.21

W2 0.96

W3 0.96

W4 0.96

W5 0.94

W6 0.93

Crel 0.92

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

85

Focussing wave group: TUD1403Foc6

0.2

W6

0 −0.2 0.2

W5

0

η[m]

−0.2 0.2

W4

0 −0.2 0.2

W3

0 −0.2 0.2

W2

0 −0.2 70

80

90

100 t[s]

110

W6

100 Breaking position [m]

S ||S influx ||∞

W5

1 W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

140

110

0

0.5

130

120

1 0.5

120

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.7: Same as Fig. A.4, now for TUD1403Foc6 case.

Table A.7: Same as Table A.4. Now for TUD1403Foc6 case.

Tp 1.89

λp 5.52

kp .a 0.12

W2 0.99

W3 0.96

W4 0.95

W5 0.96

W6 0.95

Crel 1.06

160

180

200

220

86

Supplementary files of the experiments

η[m]

Focussing wave group: TUD1403Foc7

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

70

80

90

100 t[s]

110

W6

100 Breaking position [m]

S ||S influx ||∞

W5

1 W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

140

110

0

0.5

130

120

1 0.5

120

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.8: Same as Fig. A.4, now for TUD1403Foc7 case.

Table A.8: Same as Table A.4. Now for TUD1403Foc7 case.

Tp 1.96

λp 5.89

kp .a 0.11

W2 0.99

W3 0.97

W4 0.98

W5 0.98

W6 0.97

Crel 1.13

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

87

η[m]

Focussing wave group: TUD1403Foc8

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

70

80

90

100 t[s]

110

W6

100 Breaking position [m]

S ||S influx ||∞

W5

1 W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

140

110

0

0.5

130

120

1 0.5

120

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.9: Same as Fig. A.4, now for TUD1403Foc8 case.

Table A.9: Same as Table A.4. Now for TUD1403Foc8 case.

Tp 1.96

λp 5.89

kp .a 0.13

W2 0.99

W3 0.97

W4 0.97

W5 0.97

W6 0.97

Crel 0.56

160

180

200

220

88

Supplementary files of the experiments

Focussing wave group: TUD1403Foc9

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.10: Same as Fig. A.4, now for TUD1403Foc9 case.

Table A.10: Same as Table A.4. Now for TUD1403Foc9 case.

Tp 2.16

λp 6.96

kp .a 0.17

W2 0.99

W3 0.96

W4 0.96

W5 0.96

W6 0.96

Crel 1.17

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

89

Focussing wave group: TUD1403Foc10

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.11: Same as Fig. A.4, now for TUD1403Foc10 case.

Table A.11: Same as Table A.4. Now for TUD1403Foc10 case.

Tp 2.2

λp 7.2

kp .a 0.13

W2 0.99

W3 0.97

W4 0.97

W5 0.98

W6 0.97

Crel 1.08

160

180

200

220

90

Supplementary files of the experiments

Focussing wave group: TUD1403Foc11

0.2 0 −0.2

W6

η[m]

0.2 0 −0.2

W5

0.2 0 −0.2

W4

0.2 0 −0.2

W3

0.2 0 −0.2

W2

60

70

80

90 t[s]

100

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

90 80 70 60 50 40

1 0.5

120

120

1 0.5

110

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.12: Same as Fig. A.4, now for TUD1403Foc11 case.

Table A.12: Same as Table A.4. Now for TUD1403Foc11 case.

Tp 2.2

λp 7.2

kp .a 0.16

W2 0.99

W3 0.97

W4 0.98

W5 0.98

W6 0.98

Crel 1.21

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

91

Focussing wave group: TUD1403Foc12 (non breaking)

W6

0.1 0 −0.1

W5

0.1 0

η[m]

−0.1 W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

0.1 0 −0.1 60

70

80

90

100 t[s]

1

2

3

4 ω [rad/s]

110

120

130

140

7

8

1 0.5

W6

0

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5

W2

0 0

5

6

Figure A.13: Same as Fig. A.4, now for TUD1403Foc12 case.

Table A.13: Same as Table A.4. Now for TUD1403Foc12 case.

Tp 2.38

λp 8.26

kp .a 0.06

W2 0.97

W3 0.96

W4 0.97

W5 0.97

W6 0.97

Crel 1.70

92

Supplementary files of the experiments

Focussing wave group: TUD1403Foc13

0.2

W5

0 −0.2

η[m]

0.2

W4

0 −0.2 0.2

W3

0 −0.2 0.2

W2

0 −0.2 60

70

80

90

100 t[s]

110

120

130

140

120

W5

110

Breaking position [m]

S ||S influx ||∞

100

1 W4 0.5 0 W3

1

80 70 60 50 40

W2 0.5 0 0

90

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.14: Same as Fig. A.4, now for TUD1403Foc13 case.

Table A.14: Same as Table A.4. Now for TUD1403Foc13 case.

Tp 2.4

λp 8.25

kp .a 0.14

W2 0.98

W3 0.96

W4 0.95

W5 0.96

Crel 2.44

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

93

η[m]

Bichromatic wave: TUD1403Bi2

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120

140

160

180

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.15: Same as Fig. A.4, now for TUD1403Bi2 case.

Table A.15: Same as Table A.4. Now for TUD1403Bi2 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.20

W2 0.93

W3 0.88

W4 0.86

W5 0.83

W6 0.67

Crel 2.3

160

180

200

220

94

Supplementary files of the experiments

η[m]

Bichromatic wave: TUD1403Bi3

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120

140

160

180

t[s] 120

1 0.5

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

80 70 60 50 40

1 0.5

90

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20

60

80

100

120 time [s]

Figure A.16: Same as Fig. A.4, now for TUD1403Bi3 case.

Table A.16: Same as Table A.4. Now for TUD1403Bi3 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.3

W2 0.96

W3 0.90

W4 0.87

W5 0.84

W6 0.78

Crel 3.2

140

160

180

A.3 Comparison of experiments and a-posteriori simulations

95

Bichromatic wave: TUD1403Bi4

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 60

80

100

120

140 t[s]

160

200

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.17: Same as Fig. A.4, now for TUD1403Bi4 case

Table A.17: Same as Table A.4. Now for TUD1403Bi4 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.36

W2 0.93

W3 0.82

W4 0.79

W5 0.75

W6 0.63

Crel 3.6

160

180

200

220

96

Supplementary files of the experiments

η[m]

Bichromatic wave: TUD1403Bi6

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120 t[s]

140

180

140

1 0.5

160

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.18: Same as Fig. A.4, now for TUD1403Bi6 case

Table A.18: Same as Table A.4. Now for TUD1403Bi6 case.

(T0,dt) (1.4,0.06)

λp 3.18

kp .a 0.18

W2 0.98

W3 0.94

W4 0.92

W5 0.90

W6 0.86

Crel 1.9

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

97

Bichromatic wave: TUD1403Bi7

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 50

100

150

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.19: Same as Fig. A.4, now for TUD1403Bi7 case

Table A.19: Same as Table A.4. Now for TUD1403Bi7 case.

(T0,dt) (1.7,0.06)

λp 4.3

kp .a 0.29

W2 0.98

W3 0.97

W4 0.96

W5 0.95

W6 0.92

Crel 1.4

160

180

200

220

98

Supplementary files of the experiments

Bichromatic wave: TUD1403Bi8

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.20: Same as Fig. A.4, now for TUD1403Bi8 case.

Table A.20: Same as Table A.4. Now for TUD1403Bi8 case.

(T0,dt) (1.6,0.06)

λp 3.82

kp .a 0.33

W2 0.96

W3 0.93

W4 0.93

W5 0.91

W6 0.81

Crel 2.3

160

180

200

220

A.3 Comparison of experiments and a-posteriori simulations

99

Bichromatic wave: TUD1403Bi9

0.2

W6

0 −0.2 0.2 0

η[m]

−0.2 0.2

W5

W4

0 −0.2 0.2 0 −0.2 0.2

W3

W2

0 −0.2 60

80

100

120 t[s]

140

180

140

1 0.5

160

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

Figure A.21: Same as Fig. A.4, now for TUD1403Bi9 case.

Table A.21: Same as Table A.4. Now for TUD1403Bi9 case.

(T0,dt) (1.5,0.06)

λp 3.38

kp .a 0.37

W2 0.95

W3 0.93

W4 0.91

W5 0.88

W6 0.79

Crel 3.7

160

180

200

220

100

Supplementary files of the experiments

η[m]

Irregular wave: TUD1403Ir1

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

50

100

150

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.22: Same as Fig. A.4, now for TUD1403Ir1 case.

Table A.22: Same as Table A.4. Now for TUD1403Ir1 case.

Tp 1.4

λp 3.14

kp .a 0.25

W2 0.95

W3 0.92

W4 0.91

W5 0.88

W6 0.89

Crel 7.5

200

A.3 Comparison of experiments and a-posteriori simulations

101

Irregular wave: TUD1403Ir2

0.1 W6 0 −0.1

η[m]

0.1 W5 0 −0.1 0.1 W4 0 −0.1 0.1 W3 0 −0.1 0.1 W2 0 −0.1 60

80

100

120

140 t[s]

160

180

200

220

1 0.5

W6 120

0

Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

100

80

60

40

1 0.5 0 0

W2 20

2

4

ω [rad/s]

6

8

50

10

100

150 time [s]

Figure A.23: Same as Fig. A.4, now for TUD1403Ir2 case.

Table A.23: Same as Table A.4. Now for TUD1403Ir2 case.

Tp 1.32

λp 2.74

kp .a 0.28

W2 0.91

W3 0.82

W4 0.80

W5 0.79

W6 0.66

Crel 11

200

102

Supplementary files of the experiments

Irregular wave: TUD1403Ir3

0.1 W6 0 −0.1 0.1 W5 0 −0.1

η[m]

0.1 W4 0 −0.1 0.1 W3 0 −0.1 0.1 W2 0 −0.1 60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

2

4

ω [rad/s]

6

8

10

20

50

100

150 time [s]

Figure A.24: Same as Fig. A.4, now for TUD1403Ir3 case.

Table A.24: Same as Table A.4. Now for TUD1403Ir3 case.

Tp 1.28

λp 2.57

kp .a 0.34

W2 0.77

W3 0.61

W4 0.61

W5 0.58

W6 0.53

Crel 8.1

200

A.3 Comparison of experiments and a-posteriori simulations

103

Irregular wave: TUD1403Ir4

0.2

W6

0 −0.2 0.2

W5

0

η[m]

−0.2 0.2

W4

0 −0.2 0.2

W3

0 −0.2 0.2

W2

0 −0.2 40

60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.25: Same as Fig. A.4, now for TUD1403Ir4 case.

Table A.25: Same as Table A.4. Now for TUD1403Ir4 case.

Tp 1.63

λp 4.18

kp .a 0.27

W2 0.97

W3 0.96

W4 0.96

W5 0.96

W6 0.92

Crel 1.2

200

104

Supplementary files of the experiments

η[m]

Irregular wave: TUD1403Ir7 (non breaking)

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

40

60

80

100

120 t[s]

140

160

180

200

1 0.5

W6

0

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5

W2

0 0

2

4

6 ω [rad/s]

8

10

Figure A.26: Same as Fig. A.4, now for TUD1403Ir7 case.

Table A.26: Same as Table A.4. Now for TUD1403Ir7 case.

Tp 2.6

λp 9.4

kp .a 0.15

W2 0.96

W3 0.97

W4 0.96

W5 0.96

W6 0.93

Crel 0.54

12

A.3 Comparison of experiments and a-posteriori simulations

105

Irregular wave: TUD1403Ir8

0.2 0 −0.2

η[m]

0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2

W6

W5

W4

W3

W2

40

60

80

100

120

140 t[s]

160

200

220

240

100

150

200

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

2

4

6 ω [rad/s]

8

10

12

20

50

time [s]

Figure A.27: Same as Fig. A.4, now for TUD1403Ir8 case.

Table A.27: Same as Table A.4. Now for TUD1403Ir8 case.

Tp 1.96

λp 5.87

kp .a 0.24

W2 0.97

W3 0.97

W4 0.97

W5 0.96

W6 0.95

Crel 1.7

106

Supplementary files of the experiments

Irregular wave: TUD1403Ir9

0.2 W5 0 −0.2 0.2

η[m]

W4 0 −0.2 0.2 W3 0 −0.2 0.2 W2 0 −0.2 40

60

80

100

120 t[s]

140

160

180

200

120

W5

110

Breaking position [m]

S ||S influx ||∞

100

1 W4 0.5 0 W3

1

80 70 60 50 40

W2 0.5 0 0

90

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

160

180

200

Figure A.28: Same as Fig. A.4, now for TUD1403Ir9 case. Info about breaking in experiment missing.

Table A.28: Same as Table A.4. Now for TUD1403Ir9 case.

Tp 1.96

λp 5.87

kp .a 0.24

W2 0.98

W3 0.97

W4 0.96

W5 0.96

Crel 1.87

220

A.3 Comparison of experiments and a-posteriori simulations

107

Irregular wave: TUD1403Ir10

0.2 0 −0.2 0.2

η[m]

0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0

W6

W5

W4

W3

W2

−0.2 40

60

80

100

120

140

160

180

200

220

t[s]

120

1 0.5

W6

110

0

100 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

0 0

80 70 60 50 40

1 0.5

90

W2

30

1

2

3

4 ω [rad/s]

5

6

7

8

20 100

150

200 time [s]

Figure A.29: Same as Fig. A.4, now for TUD1403Ir10 case.

Table A.29: Same as Table A.4. Now for TUD1403Ir10 case.

Tp 1.8

λp 5.02

kp .a 0.27

W2 0.97

W3 0.96

W4 0.95

W5 0.94

W6 0.86

Crel 1.11

250

108

Supplementary files of the experiments

Irregular wave: TUD1403Ir11

0.2 0 −0.2

η[m]

0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2 0.2 0 −0.2

W6

W5

W4

W3

W2

60

80

100

120

140 t[s]

160

200

220

140

1 0.5

180

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20 20

40

60

80

100

120 140 time [s]

160

180

200

Figure A.30: Same as Fig. A.4, now for TUD1403Ir11 case. Info about breaking in experiment missing.

Table A.30: Same as Table A.4. Now for TUD1403Ir11 case.

Tp 2.08

λp 6.55

kp .a 0.23

W2 0.97

W3 0.96

W4 0.96

W5 0.95

W6 0.94

Crel 1.8

220

A.3 Comparison of experiments and a-posteriori simulations

109

Soliton on Finite Background: TUD1403SFB1

0.1

W6

0 −0.1 0.1

W5

0 −0.1

η[m]

0.1

W4

0 −0.1 0.1

W3

0 −0.1 0.1

W2

0 −0.1 60

80

100

120

140

160

180

200

t[s] 140

1 0.5

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.31: Same as Fig. A.4, now for TUD1403SFB1 case.

Table A.31: Same as Table A.4. Now for TUD1403SFB1 case.

Tp 1.3

λp 2.65

kp .a 0.17

W2 0.98

W3 0.88

W4 0.89

W5 0.89

W6 0.77

Crel 1.9

200

110

Supplementary files of the experiments

η[m]

Soliton on Finite Background: TUD1403SFB2

0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

40

60

80

100

120 t[s]

140

180

200

140

1 0.5

160

W6 120

0 Breaking position [m]

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5 0 0

100

80

60

40

W2

1

2

3

4 ω [rad/s]

5

6

7

8

20

50

100

150 time [s]

Figure A.32: Same as Fig. A.4, now for TUD1403SFB2 case.

Table A.32: Same as Table A.4. Now for TUD1403SFB2 case.

Tp 1.5

λp 3.53

kp .a 0.26

W2 0.97

W3 0.91

W4 0.91

W5 0.89

W6 0.88

Crel 3.2

200

A.3 Comparison of experiments and a-posteriori simulations

111

η[m]

Harmonic focussing: TUD1403HF2 (non breaking) 0.1 0 −0.1

W6

0.1 0 −0.1

W5

0.1 0 −0.1

W4

0.1 0 −0.1

W3

0.1 0 −0.1

W2

60

80

100

120

140

160

t[s]

1 0.5

W6

0

S ||S influx ||∞

W5

1 0.5

W4

0 W3

1 0.5

W2

0 0

1

2

3

4 ω [rad/s]

5

6

7

Figure A.33: Same as Fig. A.4, now for TUD1403HF2 case.

Table A.33: Same as Table A.4. Now for TUD1403HF2 case.

Tp 2.29

λp 7.7

kp .a 0.14

W2 0.99

W3 0.97

W4 0.97

W5 0.97

W6 0.97

Crel 2.2

8

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Acknowledgments

The research presented in this dissertation has been carried out over the past 4 years in the Applied Analysis (AA) group, Department of Applied Mathematics, University of Twente (UT). It is largely inspired and encouraged by my supervisor, family, friends and colleagues whom I would like to acknowledge. First and foremost, I would like to express sincere gratitude to my supervisor, Prof. E. (Brenny) van Groesen, who I am indebted to for many things. I met Brenny for the first time when I applied an internship position at LabMath-Indonesia (LMI) in June 2011. At that time, i was finishing my master thesis. After I graduated, He offered me a position to pursue PhD degree at University of Twente and never thought before that the opportunity would bring me this far. I am thankful to him for the attentive guidance, fruitful discussions and the continuous support. His significant role helped me in finishing this dissertation. Again, I am grateful to him for giving me an opportunity to work as a post-doctoral researcher at UT and LMI starting from 1 February 2016. I would like to pronounce my sincere thanks to Prof. Stephan van Gils, the chair of AA group, for the opportunity to work in his group, and also his willingness to be one of my graduation committee. I would also like to thank other members of my graduation committee: Prof. Frederic Dias, Prof. Rene Huijsmans, Prof. Arthur Veldman, Prof. Bayu Jayawardhana, and Dr. Tim Bunnik for agreeing in the committee and for reviewing my thesis. I would also thank Prof. Peter Apers as the chairperson and the secretary of my graduation committee. I would also like to express my gratitude to Prof. Rene Huijsmans for giving me an excellent opportunity to conduct the wave breaking experiments in a wave tank at Technical University of Delft. All support during the experiments from his group member: Peter Poot, Peter Naaijen and Toni van den Munckhof are greatly appreciated. I thank MARIN for the use of the data, and in particular Dr. Tim Bunnik for discussions about the results and the organisation of the meetings. I wish to express my thanks to Dr. Andonowati for providing me a nice research atmosphere during short visits at LMI. In LMI, I met many people with whom I can discuss about everything. I thank Didit, Andreas, Hafizh, Liam, Mourice, Meirita,

Andy, Nugrahinggil, Abrari, Lia, Januar, Lawrance and others. Many friends and colleagues in the Department of Applied Mathematics have shown a great help to my academic life at campus. A special word of thanks goes to the secretaries Marielle and Linda for all the administrative arrangements. I thank Gerard Jeurnink for involving me in educational activities. Thanks to everyone who I have shared my office with: Arnida, Anastasia, Elena, Devashish, Jurgen, Leonie, Freekjan. I would also like to thank the other members of the group: Huan, Lulu, Deepak, Edo, Bettina, Edson, Felix, Wilbert, Tatyana, and others. I am really grateful for being surrounded by many warmhearted people during my stay in Enschede. I thank tante Soefiyati Hardjosumarto and Inggrid Proost for their kindness and for countless invitation to their house. I wish to express my thanks to Erwin vonk, Esther, Wisnu, Wenny, and Nida. I am also very thankful to all member of Indonesian Student Association in Enschede (PPIE) whom I cannot name one by one, which made my stay in Enschede enjoyable. I am grateful to my family especially my sisters: Chiely, Inalia and Dian for their support. I am truly grateful to my parents, Handreas Syamdiputra and Herliana Taniman for their unconditional love, prayer and support. Finally, I thank my wife, Erika Tivarini for her love and support. Above all, I thank God for His grace and guidance in my life.

About the author

Ruddy Kurnia was born on the 1th of May 1987 in Bandung, Indonesia. He obtained a degree of Bachelor of Science from Physics department of Institut Teknologi Bandung (ITB), Indonesia in July 2009 on a subject of electromagnetic method for geophysics exploration. In August 2009, he started his Master’s study on double degree program of computational science at Kanazawa University, Japan and Institut Teknologi Bandung, Indonesia. He finished his study in August 2011, on a subject of particle methods for computational fluid dynamics. From June 2011 to January 2012, he worked as an internship student at LabmathIndonesia on a subject of water wave modelling. In February 2012, he started his Ph.D research in Applied Analysis group, Department of Applied Mathematics, University of Twente. After 4 years, he finished his doctoral study which the result of his research is presented in this dissertation. Starting from 1 February 2016, he works as a post-doctoral researcher at University of Twente and Labmath-Indonesia. In this project, he is extending the applicability of the HAWASSI software.